Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Whoever buys a goat whose milk has been held back and milks it: if he likes it, he may keep it; if he dislikes it, he should give a sa' of dates in exchange for its milk."
(b) Imam al-Bukhari (may Allah have mercy on him) said that some narrate from Ibn Sirin: "a sa' of dates."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب البيوع / 10716