Musnad Ahmad 25:343

Abu al-Yaman narrated to us, Isma'il ibn 'Ayyash narrated to us, from Tha'labah ibn Muslim al-Khath'ami, from Abu Ka'b, the freed slave of Ibn 'Abbas, from Ibn 'Abbas, from the Prophet, may Allah bless him and grant him peace, that it was said to him: "O Messenger of Allah, Gabriel, peace be upon him, has been slow in coming to you." He said: "And why should he not be slow in coming to me, while you are around me, not brushing your teeth, not clipping your nails, not trimming your mustaches, and not cleaning your knuckles?"