The Prophet ﷺ said, "Don't keep camels and sheep unmilked for a long time, for whoever buys such an animal has the option to milk it and then either to keep it or return it to the owner along with one Sa of dates." Some narrated from Ibn Seereen (that the Prophet ﷺ had said), "One Sa of wheat, and he has the option for three days." And some narrated from Ibn Seereen, " ... a Sa of dates," not mentioning the option for three days. But a Sa of dates is mentioned in most narrations.  

عَنِ النَّبِيِّ ﷺ لاَ تُصَرُّوا الإِبِلَ وَالْغَنَمَ فَمَنِ ابْتَاعَهَا بَعْدُ فَإِنَّهُ بِخَيْرِ النَّظَرَيْنِ بَعْدَ أَنْ يَحْتَلِبَهَا إِنْ شَاءَ أَمْسَكَ وَإِنْ شَاءَ رَدَّهَا وَصَاعَ تَمْرٍ وَيُذْكَرُ عَنْ أَبِي صَالِحٍ وَمُجَاهِدٍ وَالْوَلِيدِ بْنِ رَبَاحٍ وَمُوسَى بْنِ يَسَارٍ عَنْ أَبِي هُرَيْرَةَ عَنِ النَّبِيِّ ﷺ صَاعَ تَمْرٍ وَقَالَ بَعْضُهُمْ عَنِ ابْنِ سِيرِينَ صَاعًا مِنْ طَعَامٍ وَهْوَ بِالْخِيَارِ ثَلاَثًا وَقَالَ بَعْضُهُمْ عَنِ ابْنِ سِيرِينَ صَاعًا مِنْ تَمْرٍ وَلَمْ يَذْكُرْ ثَلاَثًا وَالتَّمْرُ أَكْثَرُ  

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).  

مَنِ اشْتَرَى شَاةً مُحَفَّلَةً فَرَدَّهَا فَلْيَرُدَّ مَعَهَا صَاعًا وَنَهَى النَّبِيُّ ﷺ أَنْ تُلَقَّى الْبُيُوعُ  

Messenger of Allah ﷺ said, "Do not go forward to meet the caravan (to buy from it on the way before it reaches the town). And do not urge buyers to cancel their purchases to sell them (your own goods) yourselves, and do not practice Najsh. A town dweller should not sell the goods for the desert dweller. Do not leave sheep unmilked for a long time, when they are on sale, and whoever buys such an animal has the option of returning it, after milking it, along with a Sa of dates or keeping it. it has been kept unmilked for a long period by the seller (to deceive others).  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ لاَ تَلَقَّوُا الرُّكْبَانَ وَلاَ يَبِيعُ بَعْضُكُمْ عَلَى بَيْعِ بَعْضٍ وَلاَ تَنَاجَشُوا وَلاَ يَبِيعُ حَاضِرٌ لِبَادٍ وَلاَ تُصَرُّوا الْغَنَمَ وَمَنِ ابْتَاعَهَا فَهْوَ بِخَيْرِ النَّظَرَيْنِ بَعْدَ أَنْ يَحْتَلِبَهَا إِنْ رَضِيَهَا أَمْسَكَهَا وَإِنْ سَخِطَهَا رَدَّهَا وَصَاعًا مِنْ تَمْرٍ