Musnad Ahmad 1017:64

Zayd narrated to us, Husayn narrated to me, Abdullah ibn Buraydah narrated to me, he said: I heard my father, Buraydah, saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: "In the human being are three hundred and sixty joints, and upon him is to give a charity for every one of them." They said: "And who is capable of that, O Messenger of Allah?" He said: "The phlegm in the mosque that you bury, or the thing that you remove from the road. If you are not able, then two rak'ahs of the forenoon (Duha) prayer will suffice you."