It was narrated from Abu Hurairah that the Prophet said:"Do not go out to meet the riders, and do not bind the udders of camels and seep. Whoever has boughty anything in that manner has two choices: If he whishes he may keep it, or if he wants to return it he may return it, along with a Sa of dates." (Sahih )
أَخْبَرَنَا مُحَمَّدُ بْنُ مَنْصُورٍ، قَالَ حَدَّثَنَا سُفْيَانُ، عَنْ أَبِي الزِّنَادِ، عَنِ الأَعْرَجِ، عَنْ أَبِي هُرَيْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " لاَ تَلَقُّوا الرُّكْبَانَ لِلْبَيْعِ وَلاَ تُصَرُّوا الإِبِلَ وَالْغَنَمَ مَنِ ابْتَاعَ مِنْ ذَلِكَ شَيْئًا فَهُوَ بِخَيْرِ النَّظَرَيْنِ فَإِنْ شَاءَ أَمْسَكَهَا وَإِنْ شَاءَ أَنْ يَرُدَّهَا رَدَّهَا وَمَعَهَا صَاعُ تَمْرٍ " .
Nesai
The Book of Financial Transactions • Hadith 4487