Sahih Al Bukhari Hadith Number 1507

Narrated `Abdullah bin `Umar: The Prophet (peace be upon him) 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.

24  Obligatory Charity Tax (Zakat)
Hadith number 1507
Volume no 2
Chapter: 74 (Sadaqat-ul-Fitr is one Sa’ of dates (per head)