Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Quraysh said to the Prophet (peace and blessings be upon him): Pray to your Lord to turn (the hill of) al-Safa into gold for us, and then we will believe in you. He (peace and blessings be upon him) said: "Very well, but will you really do so?" They said: Yes! (We will believe.) He (peace and blessings be upon him) prayed, and Jibril (peace be upon him) came to him and said: Allah Almighty sends you greetings of peace and says: If you (peace and blessings be upon him) wish, al-Safa will be turned into gold, and then whoever disbelieves after that, I will punish him with a punishment so severe that I will not punish anyone of the creation with the like of it; and if you wish, I will open for them the door of repentance and mercy. He (peace and blessings be upon him) said: "(O Allah,) open the door of repentance and mercy (and do not turn al-Safa into gold)."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 17732