The Book of Faith (Kitab Al-Iman)
Muslim :: Book 1 : Hadith 48
It is narrated on the authority of Mu'adh b. Jabal that the Messenger of Allah (may peace be upon him) said: Mu'adh, do you know the right of Allah over His bondsmen? He (Mu'adh) said: Allah and His Apostle know best. He (the Messenger of Allah) said: That Allah alone should be worshipped and nothing should be associated with Him. He (the Holy Prophet) said: What right have they (bondsmen) upon Him in case they do it? He (Mu'adh) said: Allah and His Apostle know best. He (the Holy Prophet) said: That He would not punish them.