Sahih Muslim Book 4, Hadith 70
Ka'b b. 'Ujra met me and said: Should I not offer you a present (and added): The Messenger of Allah (ﷺ) came to us and we said: We have learnt how to invoke peace upon you; (kindly tell us) how we should bless you. He (the Holy Prophet) said: Say:" O Allah: bless Muhammad and his family as Thou didst bless the family of Ibrahim. Verily Thou art Praiseworthy and Glorious, O Allah."
We were sitting in the company of Sa'id b. 'Ubida when the Messenger of Allah (ﷺ) came to us. Bashir b. S'ad said: Allah has commanded us to bless you. Messenger of Allah! But how should we bless you? He (the narrator) said: The Messenger of Allah (ﷺ) kept quiet (and we were so much perturbed over his silence) that we wished we had not asked him. The Messenger of Allah (ﷺ) then said: (For blessing me) say:" 0 Allah, bless Muhammad and the members of his household as Thou didst bless the mernbers of Ibrahim's household. Grant favours to Muhammad and the members of his household as Thou didst grant favours to the members of the household of Ibrahim in the world. Thou art indeed Praiseworthy and Glorious" ; and salutation as you know.
" Should I not offer you a present?"