Musnad Ahmad 937:186

'Arim and 'Affan narrated to us, they said: Mahdi ibn Maymun narrated to us, from Wasil, the freed slave of Abu 'Uyaynah, from Yahya ibn 'Aqil, from Yahya ibn Ya'mar, from Abu al-Aswad al-Du'ali, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "Upon every joint of one of you, there is a charity every morning. Every glorification (tasbihah) is a charity, every declaration of oneness (tahlilah) is a charity, every declaration of greatness (takbirah) is a charity, and every declaration of praise (tahmidah) is a charity. Enjoining good is a charity, and forbidding evil is a charity. And two rak'ahs that one of you prays during the forenoon (Duha) suffice for all of that."