Musnad Ahmad 25:328

'Abd al-Rahman narrated to us, Sufyan narrated to us, from Salamah ibn Kuhayl, from 'Imran Abu al-Hakam, from Ibn 'Abbas, who said: Quraysh said to the Prophet, peace and blessings of Allah be upon him: "Call upon your Lord for us that He may make al-Safa gold for us, and we will believe in you." He said: "And will you do so?" They said: "Yes." He said: So he supplicated, and Gabriel came to him and said: "Indeed, your Lord sends you greetings of peace and says: 'If you wish, al-Safa will become gold for them; then whoever disbelieves after that among them, I will punish him with a punishment that I have not punished anyone among the worlds with. And if you wish, I will open for them the door of repentance and mercy.'" He said: "Rather, the door of repentance and mercy."