Sahih (Sahih al-Bukhari)
حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا مُعْتَمِرٌ، قَالَ سَمِعْتُ أَبِي يَقُولُ، حَدَّثَنَا أَبُو عُثْمَانَ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ ـ رضى الله عنه ـ قَالَ مَنِ اشْتَرَى شَاةً مُحَفَّلَةً، فَرَدَّهَا فَلْيَرُدَّ مَعَهَا صَاعًا. وَنَهَى النَّبِيُّ صلى الله عليه وسلم أَنْ تُلَقَّى الْبُيُوعُ.
Narrated `Abdullah bin Mas`ud:Whoever buys a sheep which has not been milked for a long time, has the option of returning it along with one Sa of dates; and the Prophet (ﷺ) forbade going to meet the seller on the way (as he has no knowledge of the market price and he may sell his goods at a low price)