Praise be to Allaah.

The rights that one Muslim has over another are many, some of which are individual obligations that are required of each person, and if he fails to do them he is sinning. Others are communal obligations; if some people do them, the burden of sin is waived for the rest. And some are mustahabb (encouraged) but not obligatory, so the Muslim is not sinning if he does not do them. 

Al-Bukhaari (1240) and Muslim (2162) narrated that Abu Hurayrah (may Allah be pleased with him) said: I heard the Messenger of Allah (blessings and peace of Allah be upon him) say: “The rights of one Muslim over another are five: returning the greeting of salaam, visiting the sick, attending funerals, accepting invitations, and saying yarhamuk Allah (may Allah have mercy on you) to one who sneezes.” 

And Muslim (2162) narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (blessings and peace of Allah be upon him) said: “The rights of one Muslim over another are six.” It was said: What are they, O Messenger of Allaah? He said: “If you meet him, greet him with salaam; if he invites you, accept the invitation; if he asks for advice, give him sincere advice; if he sneezes and praises Allaah, say Yarhamuk Allaah (may Allaah have mercy on you); if he falls sick, visit him; and if he dies, attend his funeral.” 

Ash-Shawkaani (may Allah have mercy on him) said: What is meant by the words “The rights of the Muslim” is that they should not be omitted and doing them is either obligatory, or recommended to such an extent that it is very similar to being obligatory and should not be omitted. The word “right” (haqq) may be used in the sense of obligatory, as was mentioned by Ibn al-A‘raabi.

End quote from Nayl al-Awtaar, 4/21 

1.

Returning the greeting of salaam is obligatory if the greeting is given to one person. If it is given to a group, then it is obligatory upon the group (fard kifaayah or communal obligation; if one of the group returns the greeting, the obligation as been met). With regard to initiating the greeting, the basic principle is that it is Sunnah. It says in al-Mawsoo‘ah al-Fiqhiyyah (11/314): 

Initiating the greeting is Sunnah mu’akkadah (a confirmed Sunnah) because the Prophet (blessings and peace of Allah be upon him) said: “Spread the greeting of salaam amongst yourselves.” It is obligatory to return the greeting if it is given to one person. If the greeting is given to a group, then in their case responding is a fard kifaayah (communal obligation); if one of them responds the sin is waived from the others, but if they all respond, they have all done what is required, Whether they respond all together or one after another. If they all refrain from responding, then they are all sinning because of the report which says: “The rights of one Muslim over another are five: returning (the greeting) of salaam…”

End quote. 

2.

Visiting the sick it is a communal obligation. Shaykh Ibn ‘Uthaymeen said: 

Visiting the sick is a fard kifaayah (communal obligation). 

Majmoo‘ Fataawa wa Rasaa’il Ibn ‘Uthaymeen, 13/1085 

See also the answer to question no. 71968

3.

Attending funerals is also a fard kifaayah (communal obligation). See the answer to question no. 67576 

4.

With regard to accepting invitations, if the invitation is to a wedding feast, then the majority of scholars are of the view that it is obligatory to accept unless there is a legitimate shar‘i reason not to do so. If it is for something other than a wedding feast, the majority are of the view that it is mustahabb. But there are conditions for accepting invitations in general terms. For details of that please see the answer to question no. 22006 

5.

With regard to saying Yarhamuk Allah (May Allah have mercy on you) to one who sneezes, there is a difference of opinion concerning the ruling. 

It says in al-Mawsoo‘ah al-Fiqhiyyah, 4/22: 

This saying Yarhamuk Allah (May Allah have mercy on you) is Sunnah according to the Shaafa‘is. 

According to the Hanbalis and the Hanafis, it is obligatory. 

The Maalikis said – and it is an opinion among the Hanbalis – that it is a communal obligation. It was narrated from al-Bayaan that the stronger view is that it is an individual obligation (fard ‘ayn), because of the hadeeth: “It is the duty of every Muslim who hears him (the one who sneezes) to say: Yarhamuk Allah (may Allah have mercy on you). End quote 

The more correct opinion is that it is obligatory on the one who hears the sneezer praise Allah (by saying “Al-hamdu Lillah”), because of the report narrated by al-Bukhaari (6223) from Abu Hurayrah (may Allah be pleased with him) from the Prophet (blessings and peace of Allah be upon him) who said: “Allaah likes the act of sneezing and dislikes the act of yawning, so if any one of you sneezes and praises Allaah (says ‘al-hamdu Lillaah’), it is a duty on every Muslim who hears him to say to him, ‘Yarhamuk Allaah (may Allaah have mercy on you).’” 

Ibn al-Qayyim (may Allah have mercy on him) said: We have quoted above the hadeeth of Abu Hurayrah, in which it says: “if any one of you sneezes and praises Allaah (says ‘al-hamdu Lillaah’), it is a duty (haqq) on every Muslim who hears him to say to him, ‘Yarhamuk Allaah (may Allaah have mercy on you).”. al-Tirmidhi included the hadeeth of Anas under the heading: Chapter on what was narrated about it being obligatory to say Yarhamuk Allah (may Allah have mercy on you) when one who sneezes says Al-hamdu Lillah (Praise be to Allah). This indicates that it is obligatory in his view, and this is the correct view, because of the hadeeths that clearly indicate that it is obligatory and there was nothing to contradict that, and Allah knows best. 

One of them is the hadeeth of Abu Hurayrah mentioned above, and another is his other hadeeth, “There are five (rights) that the Muslim has over his brother,” which is also mentioned above. Another is the hadeeth of Saalim ibn ‘Ubayd, in which it says: “Let those who are with him say to him: Yarhamuk Allah (may Allah have mercy on you).” And another is the report narrated by at-Tirmidhi from ‘Ali who said: The Messenger of Allah (blessings and peace of Allah be upon him) said: “The Muslim has six (rights) over his fellow-Muslim: he should greet him with salaam when he meets him; he should respond when he invites him; he should say Yarhamuk Allah (may Allah have mercy on you) if he sneezes; he should visit him if he falls sick; he should attend his funeral if he dies; and he should love for him what he loves for himself.” He (at-Tirmidhi) said: This is a hasan hadeeth. It was also narrated via another isnaad from the Prophet (blessings and peace of Allah be upon him). Some of the scholars spoke negatively about al-Haarith al-A‘war (one of the narrators). In the same chapter it is also narrated from Abu Hurayrah, Abu Ayyoob, al-Bara’ and Abu Mas‘ood. And another of these hadeeths is that which was narrated by at-Tirmidhi from Abu Ayyoob, according to which the Messenger of Allah (blessings and peace of Allah be upon him) said: “If one of you sneezes, let him say Al-hamdu Lillah (praise be to Allah); and let him say ‘ala kulli haal (in all circumstances). And let the one who responds to him say: Yarhamuk Allah (may Allah have mercy on you). And let him say: Yahdikum Allahu wa yuslih baalakum (May Allah guide you and set your affairs straight). 

There are four kinds of proof in the hadeeth quoted above (“if any one of you sneezes and praises Allaah (says ‘al-hamdu Lillaah’), it is a duty (haqq) on every Muslim who hears him to say to him, ‘Yarhamuk Allaah (may Allaah have mercy on you)”):

(i)                there is a clear statement that it is obligatory to say Yarhamuk Allah (may Allah have mercy on you), which cannot be interpreted in any other way;

(ii)              it is made obligatory by use of the word haqq (translated above as duty);

(iii)            it is made obligatory by use of the word ‘ala (on). This word clearly means that it is obligatory

(iv)            it is enjoined. There can be no doubt that there are many duties that are proven to be obligatory on the basis of less evidence than this. And Allah knows best. 

End quote from Haashiyat Ibn al-Qayyim ‘ala Sunan Abi Dawood, 13/259 

He also said: The apparent meaning of the hadeeth mentioned above is that saying Yarhamuk Allah is an individual obligation upon everyone who hears the one who sneezed say Al-hamdu Lillah; it is not acceptable for just one of them to say it. This is one of the two scholarly opinions, which was favoured by the Maalikis Ibn Abi Zayd and Abu Bakr ibn al-‘Arabi, and it cannot be otherwise. 

End quote from Zaad al-Ma‘aad, 2/437 

6.

With regard to giving him advice if he asks for it, it is most likely that offering advice is a communal obligation. 

Ibn Muflih (may Allah have mercy on him) said: 

The apparent meaning of the words of Ahmad and our companions is that it is obligatory to offer advice to the Muslim, even if he does not ask for it, as is the apparent meaning of the reports. 

End quote from al-Adaab ash-Shar‘iyyah by Ibn Muflih, 1/307 

Al-Mullah ‘Ali al-Qaari (may Allah have mercy on him) said: 

“If he asks you for advice” means if he asks you for advice, then give it to him; it is obligatory. It is also obligatory to give advice even if he did not ask for it. 

End quote from Mirqaat al-Mafaateeh, 5/213 

al-Haafiz Ibn Hajar (may Allah have mercy on him) said: 

It is clear that what is meant by “duty” (haqq) here is that it is obligatory. This is different from the words of Ibn Battaal who said that what is meant is the duty of respect and companionship. It seems that what is meant here is that it is a communal obligation. 

End quote from Fath al-Baari, 3/113 

And Allah knows best.