Narrated Abu Hurairah:
That the Prophet (ﷺ) said:   Whoever purchases an animal that has not been milked, then he retains the option for three days. If he returns it, then he is to return with it a Sa' of food, not Samra'   
[Abu 'Eisa said:] The meaning of   Not Samra'   is   not wheat.  
This Hadith is Hasan Sahih. This Hadith is acted upon according to our companions, among them Ash-Shafi'i, Ahmad, and Ishaq.