Allāhumma lā tu'ākhidhnī bimā yaqūlūn,
waghfir lī mā lā ya`lamūn
[waj`alnī khayran mimmā yaẓunnūn].
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].
Reference:
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.