Sunan an-Nasa'i, Volume 2, Book 13, Hadith 1287 (DarusSalam) ⓘ
It was narrated that Abu Mas'ud Al-Ansari said: "It was said to the Prophet: We have been commanded to send salah and salams upon you. We know how to send salams, but how should we send salah?' He said: Say: 'Alahumma salli 'ala Muhammad wa 'ala ali Muhammad, kama sallaita 'ala Ibrahima wa barik 'ala Muhammad kama barakta 'ala ali Ibrahim fil-'alamin, innaka hamidun majid (O Allah, send salah upon Muhammad and upon the family of Muhammad, as You sent salah upon the family of Ibrahim).'"
أَخْبَرَنَا زِيَادُ بْنُ يَحْيَى، قَالَ حَدَّثَنَا عَبْدُ الْوَهَّابِ بْنُ عَبْدِ الْمَجِيدِ، قَالَ حَدَّثَنَا هِشَامُ بْنُ حَسَّانَ، عَنْ مُحَمَّدٍ، عَنْ عَبْدِ الرَّحْمَنِ بْنِ بِشْرٍ، عَنْ أَبِي مَسْعُودٍ الأَنْصَارِيِّ، قَالَ قِيلَ لِلنَّبِيِّ صلى الله عليه وسلم أُمِرْنَا أَنْ نُصَلِّيَ عَلَيْكَ وَنُسَلِّمَ أَمَّا السَّلاَمُ فَقَدْ عَرَفْنَاهُ فَكَيْفَ نُصَلِّي عَلَيْكَ قَالَ " قُولُوا اللَّهُمَّ صَلِّ عَلَى مُحَمَّدٍ كَمَا صَلَّيْتَ عَلَى آلِ إِبْرَاهِيمَ اللَّهُمَّ بَارِكْ عَلَى مُحَمَّدٍ كَمَا بَارَكْتَ عَلَى آلِ إِبْرَاهِيمَ " .
also referenced under: Hadith 1286 (Reference) & Book 13, Hadith 108 (In-Book)