Dhikr – according to the situation - may be divided into two types:
1. Those that are restricted to a particular time, place or situation, such as those which are prescribed following the prayers, the dhikrs prescribed for morning and evening, and so on.
2. Those which are not restricted to certain circumstances, such as prayers for forgiveness which should be on the Muslim's lips morning and evening, and general tasbeeh, and so on.
With regard to those that are restricted, it is not permissible to add to their wording that is mentioned in the Qur’aan and Sunnah, or to subtract from it.
With regard to those that are not restricted to certain circumstances, there is nothing wrong with adding to or subtracting from them, although it is better to limit it to what is narrated, as it is more than sufficient.
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said:
The wording of adhkaar is to left as it is mentioned in the reports, and it has special characteristics and there is wisdom behind its format, so it is not open to analogy, so we must adhere to the wording in which they were narrated. This is the view favoured by al-Maaziri who said: we should stick to the wording that is narrated verbatim, and the reward may be dependent upon that wording. End quote. Fath al-Baari (11/112).
He said that when commenting on a hadeeth in which there is a dhikr that is limited to certain circumstances, and is not general. That is the dhikr to be recited when going to sleep: “Allaahumma aslamtu wajhi ilayk wa fawwadtu amri ilayk (O Allaah, I have submitted my face to You and I have delegated my affairs to You).
This wording – “the number of his Creation, as much as He is pleased, the weight of His Throne and the extent of His words” – is mentioned in another report along with tasbeeh:
It was narrated from Juwayriyah (may Allah be pleased with her) that the Prophet (blessings and peace of Allah be upon him) left her house one morning when he prayed Fajr, and she was in her prayer-place, then he came back after the forenoon had come, and she was still sitting there. He said: “Are you still as you were when I left you?” She said: Yes. The Prophet (blessings and peace of Allah be upon him) said: “After I left you I said four words three times, which if they were weighed against what you have said today, they would outweigh it: Glory and praise be to Allaah, as much as the number of His creation, as much as pleases Him, as much as the weight of His Throne and as much as the ink of His words.”
According to another report:
It was narrated that Juwayriyah said: The Messenger of Allaah (blessings and peace of Allah be upon him) passed by her when he had prayed Fajr, or after he had prayed Fajr – and he mentioned a similar report, except that he said: “Glory be to Allaah as much as the number of His creation, glory be to Allaah as much as pleases Him, glory be to Allaah as much as the weight of His Throne and glory be to Allaah as much as the ink of His words.”
Narrated by Muslim (2726). See the commentary on this dhikr in al-Manaar al-Muneef by Ibn al-Qayyim (p. 34).
This wording has been narrated with regard to tasbeeh also, and there is an addition which mentions tahmeed, takbeer, tahleel and al-hawqalah:
It was narrated from ‘Aa’ishah bint Sa’d ibn Abi Waqqaas from her father that he entered with the Messenger of Allah (blessings and peace of Allah be upon him) upon a woman in front of whom were some date pits or pebbles with which she was counting tasbeeh. He said: “Shall I tell you of something that is easier for you than this and better?” He said: “Glory be to Allah as much as the number of what He has created in heaven, glory be to Allah as much as the number of what He has created on earth, glory be to Allah as much as the number of what He has created between that, glory to be Allaah as much as He us going to create, and Allah is great likewise, and praise be to Allah likewise, and there is no god but Allah likewise, and there is no power and no strength except in Allah likewise.
Narrated by Abu Dawood (no. 1500) and al0-Tirmidhi (3568); he said it is hasan ghareeb.
Imam Ibn Khuzaymah (may Allah have mercy on him) entitled the chapter in his Saheeh in which he narrated this hadeeth (1/370): Chapter on the virtue of tahmeed, tasbeeh and takbeer by referring to the great number of the creation of Allah or anything else. End quote.
Hence ‘Ata’ (may Allah have mercy on him) said:
I say at the end of every takbeer, tasbeeh, tahmeed and tahleel: there is no power and no strength except with Allah, as much as the number of Your creation, as much as pleases You, as much as the weight of Your Throne, and then I ask for my need. End quote.
Musannaf ‘Abd al-Razzaaq (1/82).
Asking for forgiveness comes under the heading of the general type of dhikr which a person should be saying all the time, and it does not matter what the person chooses for himself of what he thinks is appropriate for praying for forgiveness and hoping for forgiveness from his Lord, even if it is not narrated in particular. That includes the wording that is mentioned in this question.
If we say that there is nothing wrong with it, what we mean is that it is permissible and is not haraam, and we do not see any reason to object to it. As for the idea that it has any special virtue, or that asking for forgiveness in these words will bring reward and virtue like what is mentioned in the hadeeth of Juwayriyah quoted above, all of that are things which need specific evidence to prove this virtue.
But it is better for the one who asked the question, and this is what we prefer for him, not to preoccupy himself with seeking to recite this wording. The Prophet (blessings and peace of Allah be upon him), who is the one who prescribed this wording in the appropriate place as we have mentioned, did not teach his Companions this wording for praying for forgiveness. Rather he chose for himself a different wording:
It was narrated that Ibn ‘Umar (may Allah be pleased with him) said: We would count for the Messenger of Allah (blessings and peace of Allah be upon him) in one sitting 100 times: ‘Rabb ighfir li wa tubb ‘alayya innaka anta al-tawwaab al-raheem (O Allaah, forgive me and accept my repentance, for You are the Accepter of Repentance, Most Merciful).”
According to another report: “Innaka anta al-tawaab al-ghafoor (You are the Acceptor of Repentance, Oft-Forgiving).”
Narrated by Abu Dawood (1516) and a-Tirmidhi (3434) and others. Classed as saheeh by al-Albaani.
The Prophet (blessings and peace of Allaah be upon him) chose for us to follow his example in that.
The Messenger of Allah (blessings and peace of Allah be upon him) said: “O people, repent to Allaah, for I repent to Allaah one hundred times a day.”
In a report narrated by Ahmad (17829): “O people, repent to Allah and ask Him for forgiveness, for I repent to Allah and ask Him for forgiveness one hundred times a day.”
And he has taught us the best wording of all for praying for forgiveness:
It was narrated from Shaddaad ibn Aws (may Allah be pleased with him) from the Prophet (blessings and peace of Allah be upon him):
“The best of prayers for forgiveness is: Allaahumma anta rabbiy laa ilaaha illa anta, khalaqtani wa ana ‘abduka wa ana ‘ala ‘ahdika wa wa’dika ma astata’tu. A’oodhu bika min sharri ma sana’tu, aboo’u laka bi ni’matika ‘alayya wa aboo’u laka bi dhanbi, faghfir li fa innahu laa yaghfir al-dhunooba illa anta (O Allaah, You are my Lord, there is no god but You. You have created me and I am Your slave and I am keeping my promise and covenant to You as much as I can. I seek refuge with You from the evil of what I do. I acknowledge Your blessing and I acknowledge my sin, so forgive me, for there is none who can forgive sin except You).” He said: “Whoever says this during the day, believing in it firmly, and dies on that day before evening comes, he will be one of the people of Paradise, and whoever says it at night, believing firmly in it, and dies before morning comes, he will be one of the people of Paradise.” Narrated by al-Bukhaari (6306)
And Allah knows best.