The Book of Zakat (Kitab Al-Zakat)
Muslim :: Book 5 : Hadith 2260
Abd al-Rahman b. Auf reported: I heard Mu'awiya b. Abu Sufyan saying in an address that he had heard the Messenger of Allah (may peace be upon him) as saying: He to whom Allah intends to do good, He gives him insight into religion. And I am only the distributor while Allah is the Bestower.