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 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).

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 ﷺ أَنْ تُلَقَّى الْبُيُوعُ.