Sadaqat Al-Fitr is compulsory on a slave as well as on a free Muslim.
Narrated Ibn Umar (RA): Allah's Messenger (SAW) has made Sadaqat Al-Fitr obligatory, (and it was), either one Sa' (approx. 3 kg) of barley or one Sa' of dates (and it was enjoined) on young and old people, and on free men as well as on slaves.
