Sunnah.com reference : Book 2, Hadith 208English translation : Book 2, Hadith 315Arabic reference : Book 2, Hadith 317
Narrated Abu Mas'ud Al-Ansari (RA):
Bashir bin Sa'd said, "Allah has commanded us to invoke blessings on you, O Messenger of Allah! But how should we bless you?" Allah's Messenger (ﷺ) kept quiet (a while) and then said, "Say: 'O Allah, bless Muhammad and the members of his
family as You have blessed Ibrahim, and grant favours to Muhammad and the members of his family as You have granted favours to Ibrahim. In the worlds You are indeed Praiseworthy and Glorious.' And the Taslim is as you know.

[Reported by Muslim].
وَعَنْ أَبِي مَسْعُودٍ اَلْأَنْصَارِيِّ ‏- رضى الله عنه ‏- قَالَ : { قَالَ بَشِيرُ بْنُ سَعْدٍ: يَا رَسُولَ اَللَّهِ ! أَمَرَنَا اَللَّهُ أَنْ نُصَلِّيَ عَلَيْكَ , فَكَيْفَ نُصَلِّي عَلَيْكَ ? فَسَكَتَ , ثُمَّ قَالَ : " قُولُوا : اَللَّهُمَّ صَلِّ عَلَى مُحَمَّدٍ , وَعَلَى آلِ مُحَمَّدٍ , كَمَا صَلَّيْتَ عَلَى آلِ إِبْرَاهِيمَ , وَبَارِكْ عَلَى مُحَمَّدٍ , وَعَلَى آلِ مُحَمَّدٍ , كَمَا بَارَكْتَ عَلَى آلِ إِبْرَاهِيمَ فِي اَلْعَالَمِينَ إِنَّكَ حَمِيدٌ مَجِيدٌ .‏ وَالسَّلَامُ كَمَا عَلَّمْتُكُمْ }  رَوَاهُ مُسْلِمٌ .‏  1‏‏1 ‏- صحيح .‏ رواه مسلم ( 405 )‏ .‏