Mughirah bin Abdullah bin Abi Aqil (may Allah have mercy on him) narrates from Sayyiduna Mughirah bin Shu'bah (may Allah be pleased with him); he said: I became a guest of the Messenger of Allah (peace and blessings be upon him), and he (peace and blessings be upon him) ordered a side of ribs (meat) for me, which was roasted. He (peace and blessings be upon him) trimmed my moustache with a knife, (placing it) over a tooth-stick (siwak), and he (peace and blessings be upon him) began cutting (meat) from it (the ribs) with it (the knife). Then Bilal (may Allah be pleased with him) came to inform him of the prayer, so he (peace and blessings be upon him) put down the knife and said to him: "May your hands be covered in dust." He said: My moustache had grown long, so he (peace and blessings be upon him) trimmed it.
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 18182