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. (Using translation from Muslim 405)  

أَنَّهُ قَالَ أَتَانَا رَسُولُ اللهِ ﷺ فِي مَجْلِسِ سَعْدِ بْنِ عُبَادَةَ فَقَالَ لَهُ بَشِيرُ بْنُ سَعْدٍ أَمَرَنَا اللهُ أَنْ نُصَلِّيَ عَلَيْكَ يَا رَسُولَ اللهِ فَكَيْفَ نُصَلِّي عَلَيْكَ؟ فَسَكَتَ رَسُولُ اللهِ ﷺ حَتَّى تَمَنَّيْنَا أَنَّهُ لَمْ يَسْأَلْهُ ثُمَّ قَالَ قُولُوا اللهُمَّ صَلِّ عَلَى مُحَمَّدٍ وَعَلَى آلِ مُحَمَّدٍ كَمَا صَلَّيْتَ عَلَى آلِ إِبْرَاهِيمَ وَبَارِكْ عَلَى مُحَمَّدٍ وَعَلَى آلِ مُحَمَّدٍ كَمَا بَارَكْتَ عَلَى آلِ إِبْرَاهِيمَ فِي الْعَالَمِينَ إِنَّكَ حَمِيدٌ مَجِيدٌ وَالسَّلَامُ كَمَا قَدْ عَلِمْتُمْ