Praise be to Allaah.
You should adhere to what was narrated of the du‘aa’ of the
Prophet (blessings and peace of Allah be upon him) between the two
prostrations, which is to say, “Rabb ighfir li (Lord forgive me)”, as
it was narrated by an-Nasaa’i (1145) and Ibn Maajah (897) from Hudhayfah
(may Allah be pleased with him) that the Prophet (blessings and peace of
Allah be upon him) used to say between the two prostrations: “Rabb ighfir
li, Rabb ighfir li (Lord forgive me, Lord forgive me).”
It is proven that the Prophet (blessings and peace of Allah
be upon him) also used to say between the two prostrations: “Allaahumma
ighfir li warhamni wajburni warfa‘ni wahdini wa ‘aafini warzuqni (O
Allaah, forgive me, have mercy on me, console me, raise me in status, guide
me, grant me well being and grant me provision).”
At-Tirmidhi (284) narrated from Ibn ‘Abbaas (may Allah be
pleased with him) that the Prophet (blessings and peace of Allah be upon
him) used to say between the two prostrations: “Allaahumma ighfir li
warhamni wajburni wahdini warzuqni (O Allaah, forgive me, have mercy on
me, console me, guide me, and grant me provision).”
Abu Dawood (850) narrated it as follows: “Allaahumma
ighfir li warhamni wa ‘aafini wahdini warzuqni (O Allaah, forgive me,
have mercy on me, grant me well being, guide me and grant me provision).”
Ibn Maajah (898) narrated it as follows: “Rabb ighfir li
warhamni wajburni warzuqni warfa‘ni (O Lord, forgive me, have mercy on
me, console me, grant me provision and raise me in status).
This hadeeth was classed as saheeh by al-Albaani in Saheeh
at-Tirmidhi.
An-Nawawi (may Allah have mercy on him) said in al-Majmoo‘
(3/414): With regard to the hadeeth of Ibn ‘Abbaas, it was narrated by Abu
Dawood, at-Tirmidhi and others with a jayyid isnaad. It was narrated by
al-Haakim in al-Mustadrak and he said: Its isnaad is saheeh. He
quoted the different versions then he said: To be on the safe side, the best
option is to combine all the reports and say all the phrases mentioned, of
which there are seven: “Allaahumma ighfir li warhamni wa ‘aafini wajburni
warfa‘ni wahdini warzuqni (O Allaah, forgive me, have mercy on me, grant
me well being, console me, raise me in status, guide me and grant me
provision).” End quote.
With regard to adding to this du‘aa’, what appears to be the
case is that it is permissible, but it is preferable to keep to what has
been narrated and to offer du‘aa’ for one’s parents in prostration or before
saying the salaam at the end of the prayer. Muslim (479) narrated from Ibn
‘Abbaas (may Allah be pleased with him) that the Messenger of Allah
(blessings and peace of Allah be upon him) said: “…as for prostrating,
strive in du’aa’, for it is deserving of a response (from your Lord).”
Shaykh Ibn Baaz (may Allah have mercy on him) said: Then he
should rise from prostration, saying “Allahu akbar (Allah is most great),”
and sit muftarishan, which means sitting on the left foot and holding the
right foot upright, placing his right hand on his right thigh or on his
knee, extending his fingers over his knee, and placing his left hand on his
left thigh or his left knee, extending his fingers over it. This is the
Sunnah. And he should say: “Rabb ighfir li, Rabb ighfir li, Rabb ighfir
li (Lord forgive me, Lord forgive me, Lord forgive me), as the Messenger
(blessings and peace of Allah be upon him) used to do. And it is mustahabb
to say in addition to that: Allahumma ighfir li warhamni wahdini wajburni
warzuqni wa ‘aafini (O Allah, forgive me, have mercy on me, guide me,
console me, grant me provision and grant me well being), because that is
proven from the Prophet (blessings and peace of Allah be upon him). And if
he says more than that, there is nothing wrong with it, such as if he says,
“Allahumma ighfir li wa li waalidayya (O Allah, forgive me and my
parents)” or “Allaahumma adkhilni al-Jannah wa anjini min an-naar (O
Allah, admit me to Paradise and save me from Hell)” or “Allaahumma aslih
qalbi wa ‘amali (O Allah, make my heart and my actions righteous) and so
on. But he should ask a great deal for forgiveness between the two
prostrations, as was narrated from the Prophet (blessings and peace of Allah
be upon him).
End quote from Fataawa ash-Shaykh Ibn Baaz, 11/36
And Allah knows best.