Musnad Ahmad 30:262

Sufyan narrated to us, from Ma'mar, from Ayyub, from Ibn Sirin. It was said to Sufyan: "From Abu Hurayrah?" He said: "Yes." It was said to him: "From the Prophet, may Allah bless him and grant him peace?" He said: "Yes." "Whoever buys a *muhaffalah* (an animal whose milk has been withheld in the udder) or a *musarrah* (an animal whose milk has been withheld in the udder), he has the choice. If he wishes to return it, let him return it, and if he wishes to keep it, he may keep it."