Sunan an-Nasa'i, Hadith 3369 ⓘ
It was narrated that Muhammad bin Hatib said: "The Messenger of Allah said: 'What differentiates between the lawful and the unlawful is the Duff, and the voice (singing) for the wedding.'"
أَخْبَرَنَا مُجَاهِدُ بْنُ مُوسَى، قَالَ حَدَّثَنَا هُشَيْمٌ، عَنْ أَبِي بَلْجٍ، عَنْ مُحَمَّدِ بْنِ حَاطِبٍ، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " فَصْلُ مَا بَيْنَ الْحَلاَلِ وَالْحَرَامِ الدُّفُّ وَالصَّوْتُ فِي النِّكَاحِ " .
also referenced under: Book 26, Hadith 174 (In-Book) & Volume 4, Book 26, Hadith 3371 (DarusSalam)