Sunan an-Nasa'i, Volume 5, Book 37, Hadith 4134 (DarusSalam) ⓘ
It was narrated from Masruq that: The Messenger of Allah [SAW] said: "Do not revert to disbelievers after I am gone." It is Mursal.
أَخْبَرَنِي إِبْرَاهِيمُ بْنُ يَعْقُوبَ، قَالَ حَدَّثَنَا يَعْلَى، قَالَ حَدَّثَنَا الأَعْمَشُ، عَنْ أَبِي الضُّحَى، عَنْ مَسْرُوقٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " لاَ تَرْجِعُوا بَعْدِي كُفَّارًا " . مُرْسَلٌ .
also referenced under: Hadith 4129 (Reference) & Book 37, Hadith 164 (In-Book)