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).
Source: sunnah.com
Other translations
Arabic
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، وَابْنُ، بَشَّارٍ قَالاَ حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ عَمْرِو بْنِ مُرَّةَ، عَنْ خَيْثَمَةَ، عَنْ عَدِيِّ بْنِ حَاتِمٍ، عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم أَنَّهُ ذَكَرَ النَّارَ فَتَعَوَّذَ مِنْهَا وَأَشَاحَ بِوَجْهِهِ ثَلاَثَ مِرَارٍ ثُمَّ قَالَ " اتَّقُوا النَّارَ وَلَوْ بِشِقِّ تَمْرَةٍ فَإِنْ لَمْ تَجِدُوا فَبِكَلِمَةٍ طَيِّبَةٍ " .
sunnah.com