From Sahih Muslim (Hadith 2350):
Adi b. Hatim reported that the Messenger of Allah (ﷺ) made a mention of the Fire and sought refuge (with Allah against it). He turned aside his face three times and then said:Protect yourselves against Fire even if with half a date. But if you fail to find it (then protect yourselves against Fire) with the help of a pleasant word
Reference: Muslim 2350