For one you have insulted

Allāhumma fa'ayyumā mu'minin sababtuhu faj`al dhālika lahu qurbatan ilayka yawma ‘l-qiyāmah.

O Allah, whomever of the believers I have abused, give him the reward of a sacrificial slaughter for it on the Day of Resurrection.

[ 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. Hisn al-Muslim 230 ]