In one narration the words are: The Prophet (peace and blessings be upon him) asked him: "What prevents you from this?" He replied: "I have seen your people: they denied you, they forced you to leave, and they fought against you. So I am watching to see what becomes of you. If you prevail over them, I will believe in you and follow you, and if they prevail over you, I will not follow you." (Allamah al-Haythami says:) I say: Abu Dawud has recorded part of this report.
Abdullah bin Ahmad and his father recorded it, though they did not cite the wording of the text.
Al-Tabarani also recorded it, and the narrators of both are the narrators of the Sahih.