Musnad Ahmad 774:0

Narrated to us by Waki’, from Sufyan, from Firas, from al-Sha’bi, from ‘Adi ibn Hatim, who said: The Messenger of Allah (ﷺ) said: "Protect yourselves from the Fire, even if by half a date." He said: Then he turned his face away and said: "Protect yourselves from the Fire." Then he turned his face away—and I think he said it three times—until we thought he was looking at it. Then he said: "Protect yourselves from the Fire, even if by a good word."