Musnad Ahmad 1017:102

'Ali ibn al-Hasan ibn Shaqiq narrated to us, al-Husayn ibn Waqid informed us, 'Abdullah ibn Buraydah narrated to us, from his father, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "In a human being there are three hundred and sixty joints, and upon him is to give a charity for every joint every day." They said: "And who is capable of that, O Messenger of Allah?" He said: "The phlegm you see in the mosque, so you bury it, or the thing you remove from the road. If you are not able, then two rak'ahs of the forenoon (Duha) prayer will suffice you."