ENOfficial
It was narrated that Muhammad bin Hatib said: "The Messenger of Allah (ﷺ) said: 'What differentiates between the lawful and the unlawful is the Duff, and the voice (singing) for the wedding.'"
Source: sunnah.com
Other translations
Arabic
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 " .
sunnah.com