Recite the following aloud or silently.
“Astagh ferrullah (3 times), Allah humma antas salamu wa minkas salamu tabarakta ya thaljalalee wal ikram.”
(I ask Allah to forgive me (3 times), Oh Allah, You are the Peace, and You are the Source of Peace, You are Blessed, Oh Possessor of Glory and Honor)
Always recite the following du’as silently.
“Subhana-Allah” (33 times)
(Glory be to Allah)
“Alhamdulillah” (33 times)
(Praise be to Allah)
“Allahu Akbar” (33 times)
(Allah is the greatest)
“La ilaha illa Allahu wahdahu la shareeka lahu, lahul mulku wa lahul hamdu, wa huwa ‘ala kullee shay’in qadeer”
(There is none worthy of worship except Allah alone, no associate does He have, His is the Kingdom, to Him is All-Praise, and He is well able to do all things.) Reciting this supplication 100 times would get the reward of manumitting ten slaves, one hundred good deeds would be written for him, one hundred sins would be remitted from him, it would be a shield for him from the Shaytan that day till night, and nobody would arrive with better than what he arrived with except for one that had done more than him.
Ibn Abbas (RA) said: “I used to know the end of the Prophet’s (SAW) prayer by the takbir .” (Sahih – Al-Bukhari, Muslim, Abu Dawood, An-Nasaa’ee and Abu Awaanah)
After having ended his (SAW) salah the Messenger of Allah (SAW) used to ask for forgiveness three times (for example: Astagh Ferrullah), then he would say: “Allah humma antas salamu wa minkas salamu tabarakta ya thalijalali wal ikram.” (Sahih – Al-Bukhari, Muslim and At-Tirmithi)
It is reported by way of the Messenger of Allah (SAW) that he said: “Whoever makes tasbeeh (Subhana-Allah) after each Salat 33 times, tahmeed (Alhumdulillah) 33 times, takbir (Allahu Akbar) 33 times, and completes a hundred by saying: ‘La ilaha illa Allahu wahdahu la shareeka lahu, lahul mulku wa lahul hamdu, wa huwa ‘ala kulli shay’in qadeer.’ His sins would be forgiven even if they were as plentiful as the foam of the sea.” (Sahih – Muslim)