Sayyiduna Anas bin Malik (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) forbade selling muhaffalah animals (animals whose milk has been left in the udder to make them look like heavy milkers), and he said: Whoever buys them has the option (to cancel the sale) once he has milked them.
Al-Bazzar recorded it; its chain contains a narrator, Isma'il bin Muslim al-Makki, who is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب البيوع / 6525