(74) باب صَدَقَةِ الْفِطْرِ صَاعًا مِنْ تَمْرٍ
Narrated `Abdullah bin `Umar:
The Prophet (ﷺ) ordered (Muslims) to give one Sa' of dates or one Sa' of barley as Zakat-ul-Fitr. The people rewarded two Mudds of wheat as equal to that.
Reference: Sahih al-Bukhari 1507
In-book reference: Book 24, Hadith 108
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 2, Book 25, Hadith 583