Language:
كتاب الزكاة
24
Obligatory Charity Tax (Zakat)
(78)
Chapter: Sadaqat-ul-Fitr is obligatory on the young and the old
(78)
باب صَدَقَةِ الْفِطْرِ عَلَى الصَّغِيرِ وَالْكَبِيرِ

Narrated Ibn `Umar:

Allah's Messenger (ﷺ) has made Sadaqat-ul-Fitr obligatory, (and it was), either one Sa' of barley or one Sa' of dates (and its payment was obligatory) on young and old people, and on free men as well as on slaves.

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا يَحْيَى، عَنْ عُبَيْدِ اللَّهِ، قَالَ حَدَّثَنِي نَافِعٌ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنه ـ قَالَ فَرَضَ رَسُولُ اللَّهِ صلى الله عليه وسلم صَدَقَةَ الْفِطْرِ صَاعًا مِنْ شَعِيرٍ، أَوْ صَاعًا مِنْ تَمْرٍ عَلَى الصَّغِيرِ وَالْكَبِيرِ وَالْحُرِّ وَالْمَمْلُوكِ‏.‏
Reference : Sahih al-Bukhari 1512
In-book reference : Book 24, Hadith 113
USC-MSA web (English) reference : Vol. 2, Book 25, Hadith 588
  (deprecated numbering scheme)