Sunan an-Nasa'i, Hadith 1292 ⓘ
It was narrated that Musa bin Talha said: "I asked Zaid bin Kharijah who said: 'I asked the Messenger of Allah and he said: Send salah upon me and strive hard in supplication, and say: Alahumma salli 'ala Muhammad wa 'ala ali Muhammad (O Allah, send salah upon Muhammad and upon the family of Muhammad).'"
أَخْبَرَنَا سَعِيدُ بْنُ يَحْيَى بْنِ سَعِيدٍ الأُمَوِيُّ، فِي حَدِيثِهِ عَنْ أَبِيهِ، عَنْ عُثْمَانَ بْنِ حَكِيمٍ، عَنْ خَالِدِ بْنِ سَلَمَةَ، عَنْ مُوسَى بْنِ طَلْحَةَ، قَالَ سَأَلْتُ زَيْدَ بْنَ خَارِجَةَ قَالَ أَنَا سَأَلْتُ، رَسُولَ اللَّهِ صلى الله عليه وسلم فَقَالَ " صَلُّوا عَلَىَّ وَاجْتَهِدُوا فِي الدُّعَاءِ وَقُولُوا اللَّهُمَّ صَلِّ عَلَى مُحَمَّدٍ وَعَلَى آلِ مُحَمَّدٍ " .
also referenced under: Book 13, Hadith 114 (In-Book) & Volume 2, Book 13, Hadith 1293 (DarusSalam)