Sayyiduna Adi bin Hatim al-Ta'i (may Allah be pleased with him) says that the Messenger of Allah (peace and blessings be upon him) mentioned the Fire, sought refuge from it and turned his face away; then he mentioned it, sought refuge from it and turned his face away. Shu'bah said: As for twice, there is no doubt. Then he said: "Protect yourselves from the Fire, even if by means of a piece of a date; and if you do not find even that, then by means of a good word."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الزكاة / 7745