"The Messenger of Allah said: 'What differentiates between the lawful and the unlawful is the Duff, and the voice (singing) for the wedding.'"
Sunan an-Nasa'i Book 26, Hadith 174
← Previous Hadith "The Messenger of Allah gave permission for Mut'ah, so I and another man went to a woman from Bani 'Amir and offered ourselves to her (for Mut'ah). She said: 'What will you give me?' I said: 'My Rida' (upper garment).' My companion also said: 'My Rida'.' My companion's Rida' was finer than mine, but I was younger than him. When she looked at my companion's Rida' she liked it, but when she looked at me, she liked me. Then she said: 'You and your Rida' are sufficient for me.' I stayed with her for three (days), then the Messenger of Allah said: 'Whoever has any of these women whom he married temporarily should let them go.'"

Sunan an-Nasa'i Book 26, Hadith 173 Next Hadith → "I heard Muhammad bin Hatib say: 'What differentiates between the lawful and the unlawful is the voice (singing).'"

Sunan an-Nasa'i Book 26, Hadith 175