كتاب الزكاة
12  
The Book of Zakat
(20)
Chapter: Encouragement to give charity even if it is with half a date or a kind word. And charity is a shield against the fire.
(20)
باب الْحَثِّ عَلَى الصَّدَقَةِ وَلَوْ بِشِقِّ تَمْرَةٍ أَوْ كَلِمَةٍ طَيِّبَةٍ وَأَنَّهَا حِجَابٌ مِنْ النَّارِ
Sahih Muslim 1017 c

Mundhir b. Jarir narrated on the authority of his father:

When we were sitting in the company of the Messenger of Allah (ﷺ). There came people dressed in striped woollen clothes, and the rest of the hadith in the same, and there (it is also mentioned):" He observed the Zuhr prayer and then climbed up a small pulpit, praised Allah, lauded Him, and then said: Verily Allah in His Book has revealed: 'O people, fear your Lord, ' etc." (iv. 1).
حَدَّثَنِي عُبَيْدُ اللَّهِ بْنُ عُمَرَ الْقَوَارِيرِيُّ، وَأَبُو كَامِلٍ وَمُحَمَّدُ بْنُ عَبْدِ الْمَلِكِ الأُمَوِيُّ قَالُوا حَدَّثَنَا أَبُو عَوَانَةَ، عَنْ عَبْدِ الْمَلِكِ بْنِ عُمَيْرٍ، عَنِ الْمُنْذِرِ بْنِ جَرِيرٍ، عَنْ أَبِيهِ، قَالَ كُنْتُ جَالِسًا عِنْدَ النَّبِيِّ صلى الله عليه وسلم فَأَتَاهُ قَوْمٌ مُجْتَابِي النِّمَارِ وَسَاقُوا الْحَدِيثَ بِقِصَّتِهِ وَفِيهِ فَصَلَّى الظُّهْرَ ثُمَّ صَعِدَ مِنْبَرًا صَغِيرًا فَحَمِدَ اللَّهَ وَأَثْنَى عَلَيْهِ ثُمَّ قَالَ ‏"‏ أَمَّا بَعْدُ فَإِنَّ اللَّهَ أَنْزَلَ فِي كِتَابِهِ ‏{‏ يَا أَيُّهَا النَّاسُ اتَّقُوا رَبَّكُمُ‏}‏ الآيَةَ ‏"‏ ‏.‏
Reference : Sahih Muslim 1017c
In-book reference : Book 12, Hadith 90
USC-MSA web (English) reference : Book 5, Hadith 2221
  (deprecated numbering scheme)