Sahih Bukhari Volume 008, Book 076, Hadith Number 507.

Narated By Mu'adh bin Jabal : While I was riding behind the Prophet as a companion rider and there was nothing between me and him except the back of the saddle, he said, "O Mu'adh!" I replied, "Labbaik O Allah's Apostle! And Sa'diak!" He proceeded for a while and then said, "O Mu'adh!" I said, "Labbaik and Sa'daik, O Allah's Apostle!" He then proceeded for another while and said, "O Mu'adh bin Jabal!" I replied, "Labbaik, O Allah's Apostle, and Sa'daik!" He said, "Do you know what is Allah's right on His slaves?" I replied, "Allah and His Apostle know better." He said, "Allah's right on his slaves is that they should worship Him and not worship anything besides Him." He then proceeded for a while, and again said, "O Mu'adh bin Jabal!" I replied. "Labbaik, O Allah's Apostle, and Sa'daik." He said, "Do you know what is (Allah's) slaves' (people's) right on Allah if they did that?" I replied, "Allah and His Apostle know better." He said, "The right of (Allah's) slaves on Allah is that He should not punish them (if they did that)."