Language:
كتاب الزكاة
24
Obligatory Charity Tax (Zakat)
(77)
Chapter: Sadaqat-ul-Fitr on a slave as well as on a free Muslim
(77)
باب صَدَقَةِ الْفِطْرِ عَلَى الْحُرِّ وَالْمَمْلُوكِ
Sahih al-Bukhari 1511

Narrated Nafi`:

Ibn `Umar said, "The Prophet (ﷺ) made incumbent on every male or female, free man or slave, the payment of one Sa' of dates or barley as Sadaqat-ul-Fitr (or said Sadaqa-Ramadan)." The people then substituted half Sa' of wheat for that. Ibn `Umar used to give dates (as Sadaqat-ul-Fitr). Once there was scarcity of dates in Medina and Ibn `Umar gave barley. 'And Ibn `Umar used to give Sadaqat-ul- Fitr for every young and old person. He even used to give on behalf of my children. Ibn `Umar used to give Sadaqat-ul-Fitr to those who had been officially appointed for its collection. People used to give Sadaqat-ul-Fitr (even) a day or two before the `Id.

حَدَّثَنَا أَبُو النُّعْمَانِ، حَدَّثَنَا حَمَّادُ بْنُ زَيْدٍ، حَدَّثَنَا أَيُّوبُ، عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ قَالَ فَرَضَ النَّبِيُّ صلى الله عليه وسلم صَدَقَةَ الْفِطْرِ ـ أَوْ قَالَ رَمَضَانَ ـ عَلَى الذَّكَرِ وَالأُنْثَى، وَالْحُرِّ وَالْمَمْلُوكِ، صَاعًا مِنْ تَمْرٍ أَوْ صَاعًا مِنْ شَعِيرٍ، فَعَدَلَ النَّاسُ بِهِ نِصْفَ صَاعٍ مِنْ بُرٍّ‏.‏ فَكَانَ ابْنُ عُمَرَ ـ رضى الله عنهما ـ يُعْطِي التَّمْرَ، فَأَعْوَزَ أَهْلُ الْمَدِينَةِ مِنَ التَّمْرِ فَأَعْطَى شَعِيرًا، فَكَانَ ابْنُ عُمَرَ يُعْطِي عَنِ الصَّغِيرِ وَالْكَبِيرِ، حَتَّى إِنْ كَانَ يُعْطِي عَنْ بَنِيَّ، وَكَانَ ابْنُ عُمَرَ ـ رضى الله عنهما ـ يُعْطِيهَا الَّذِينَ يَقْبَلُونَهَا، وَكَانُوا يُعْطُونَ قَبْلَ الْفِطْرِ بِيَوْمٍ أَوْ يَوْمَيْنِ‏.‏
Reference : Sahih al-Bukhari 1511
In-book reference : Book 24, Hadith 112
USC-MSA web (English) reference : Vol. 2, Book 25, Hadith 587
  (deprecated numbering scheme)