Narrated Ibn 'Abbas:
Whenever the Prophet offered his Tahajjud prayer, he would say, "O Allah, our Lord! All the praises are for You; You are the Keeper (Establisher or the One Who looks after) of the Heavens and the...
O Allah, do not call me to account for what they say and forgive me for what they have no knowledge of [and make me better than they imagine].
Info: Al-Bukhari, Al-'Adabul-Mufrad no. 761. See Al-Albani, Sahih Al-'Adabul-Mufrad (no. 585). The portion between brackets if from Al-Bayhaqi, Shu'ab Al-Iman 4/228, and comes another account.