Sahih Bukhari, Chapter: Jihaad (Fighting for the cause of Allah)

I was a companion rider of the Prophet (SAW) on a donkey called Ufair. The Prophet (SAW) asked, "O Muadh! Do you know what Allah's right on His slaves is, and what the right of His slaves on Him is?" I replied, "Allah and His Apostle (SAW) know better." He said, "Allah's right on His slaves is that they should worship Him (Alone) and should not worship any besides Him. And slaves' right on Allah is that He should not punish him who worships none besides Him." I said, "O Allah's Apostle (SAW)! Should I not inform the people of this good news?" He said, "Do not inform them of it, lest they should depend on it (solely)."