From Sahih Bukhari (Hadith 6540):
Narrated `Adi bin Hatim:The Prophet (ﷺ) said, "Protect yourself from the Fire." He then turned his face aside (as if he were looking at it) and said again, "Protect yourself from the Fire," and then turned his face aside (as if he were looking at it), and he said so for the third time till we thought he was looking at it. He then said, "Protect yourselves from the Fire, even if with one half of a date and he who hasn't got even this, (should do so) by (saying) a good, pleasant word
Reference: Bukhari 6540