IN-45
Invocation for someone you have spoken ill to
Allaahumma fa'ayyumaa mu'minin sababtuhu faj'al thaalika lahu qurbatan 'ilayka yawmal-qiyaamati.
O Allah, whomever of the believers I have abused, give him the reward of a sacrificial slaughter for it on the Day of Resurrection.
Reference: Al-Bukhari, cf. Al-Asqalani, Fathul-Bari 11/171, Muslim 4/2007. The wording in Muslim's report is: 'make it a purification for him and a source of mercy
How a Muslim should praise another Muslim
If any of you praises his companion then let him say :
'Ahsibu fulaanan wallaahu haseebuhu
I consider (such and such a person) , and Allah is his Assessor ,
wa laa 'uzakkee 'alallaahi 'ahadan
(meaning : and I cannot claim anyone to be pious before Allah) if you know of this (good character trait in the person) to be such and such (saying what he thinks is praiseworthy in that person).
Reference: Muslim 4/2296.
What a Muslim should say when he is praised
Allaahumma laa tu'aakhithnee bimaa yaqooloona, waghfir lee maa laa ya'lamoona [waj'alnee khayram-mimmaa yadhunnoon].
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.
