Mishkat al-Masabih 2847
Abu Huraira reported God's Messenger.as saying, “Do not go out to meet riders to conduct business with them; none of you must buy in opposition to one another1, nor must you bid against one another; a townsman must not sell for a man from the desert; and do not tie up the udders of camels and sheep, for he who buys them after that has been done has two courses open to him after milking them :
he may keep them if he is pleased with them, and may return them along with a sa‘ of dates if he is displeased with them.” A version by Muslim has, “If anyone buys a sheep whose udder has been tied up he has three days in which to decide whether to keep it or not; but if he returns it he must return with it a sa’ of any grain but wheat.” 2 (Bukhari and Muslim.)

1. When agreement has obviously been reached, although the contract has not been confirmed, no one must step in and offer a higher price.
2. Samra’ . The full pharse is hinta samra’ , meaning "tawny wheat" ; then the adjective is used by itself as a word for wheat.
وَعَنْ أَبِي هُرَيْرَةَ: أَنَّ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ قَالَ: " لَا تَلَقُّوُا الرُّكْبَانَ لِبَيْعٍ وَلَا يَبِعْ بَعْضُكُمْ عَلَى بَيْعِ بَعْضٍ وَلَا تَنَاجَشُوا وَلَا يَبِعْ حَاضِرٌ لِبَادٍ وَلَا تُصَرُّوا الْإِبِلَ وَالْغَنَمَ فَمِنِ ابْتَاعَهَا بَعْدَ ذَلِكَ فَهُوَ بِخَيْرِ النَّظِرَيْنِ بَعْدَ أَنْ يحلبَها: إِنْ رَضِيَهَا أَمْسَكَهَا وَإِنْ سَخِطَهَا رَدَّهَا وَصَاعًا مِنْ تمر "
وَفِي رِوَايَةٍ لِمُسْلِمٍ: " مَنِ اشْتَرَى شَاةً مُصَرَّاةً فَهُوَ بِالْخِيَارِ ثَلَاثَةَ أَيَّامٍ: فَإِنْ رَدَّهَا رَدَّ مَعهَا صَاعا من طَعَام لَا سمراء "