Sunan Abu Dawud
3444
Sahih+3

Narrated Abu Hurairah: The Prophet (ﷺ) as saying: If anyone buys sheep whose udders have been tied up, he has option for three days: he may return it if he desires with a sa' of any grain, not (necessarily) wheat

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid