Al-Kafirun 109:6

According to the reports, a group of Quraysh notables — sources name al-Walid ibn al-Mughira, al-'As ibn Wa'il, al-Aswad ibn al-Muttalib and Umayya ibn Khalaf — proposed a compromise to the Prophet: for one year he would worship their gods, and for one year they would worship his God. Thereupon the surah was revealed, beginning "Say: O disbelievers! I do not worship what you worship, nor are you worshippers of what I worship," and ending "To you your religion, and to me mine." The surah declared in decisive terms that no bargaining is possible over the oneness of God.

Vâhidî, Esbâbü'n-Nüzûl; Taberî, Câmiu'l-beyân