Specifying a particular number of times for praying for forgiveness (istighfaar)

It is mustahabb for the
Muslim to pray for forgiveness a great deal. The Prophet (peace and
blessings of Allaah be upon him) used to pray for forgiveness one hundred
times every day and night. 

It was narrated from
al-Agharr al-Muzani (may Allaah be pleased with him) that the Messenger of
Allaah (peace and blessings of Allaah be upon him) said: “I ask Allaah
for forgiveness one hundred times a day.” Narrated by Muslim (2702).  

It was narrated from Abu
Hurayrah (may Allaah be pleased with him) that the Messenger of Allaah
(peace and blessings of Allaah be upon him) said: “I ask Allaah, may He be
glorified and exalted, for forgiveness and I repent to Him one hundred times
every day.” Narrated by al-Nasaa’i in al-Sunan al-Kubra (6/114) and
by Ahmad in al-Musnad (2/450); it was classed as hasan by the
commentators on al-Musnad. 

And Abu Hurayrah (may
Allaah be pleased with him) said: I heard the Messenger of Allaah
(peace and blessings of Allaah be upon him) say: “By Allaah, I ask Allaah
for forgiveness and I repent to Him more than seventy times every day.”
Narrated by al-Bukhaari (6307). 

It was narrated that Ibn
‘Umar (may Allaah be pleased with him) said: We used to count the Messenger
of Allaah (peace and blessings of Allaah be upon him) saying in a
single gathering one hundred times: Rabb ighfir li wa tubb ‘alayya innaka
anta al-Tawwaab al-Raheem (O Lord, forgive me and accept my repentance,
for You are the Acceptor of repentance, the Most Merciful). Narrated by Abu
Dawood (1516) and al-Tirmidhi (3430); classed as saheeh by al-Albaani in
Saheeh Abi Dawood. 

Abu Hurayrah (may Allaah be
pleased with him) said: I never saw anyone say “Astighfir Allaah wa
atoobu ilayh (I ask Allaah for forgiveness and I repent to him)” more
than the Messenger of Allaah (peace and blessings of Allaah be upon
him). Narrated by al-Nasaa’i in al-Sunan al-Kubra (6/118). 

If you want to stick to
this number (one hundred) following thereby the example of the Prophet
(peace and blessings of Allaah be upon him), then you will have the reward.
And if you want to do more than that, there is nothing wrong with it so long
as you do not choose a specific number or a specific way; rather when doing
the additional amount you should do whatever is easy for you, because it is
not prescribed to set a specific number for acts of worship if it is not
narrated in the shar’i texts. 

And Allaah knows best.