That the Prophet (ﷺ) said: "Do not go out to meet the market (caravan), do not leave animals un-milked (to deceive the buyer), nor out-spend one another." [Abu 'Eisa said:] There are narrations on this topic from Ibn Mas'ud and Abu Hurairah. The Hadith if Ibn 'Abbas is a Hasan Sahih Hadith. This is acted upon according to the people of knowledge, they dislike selling the Muhaffalah, and it is the Musarrah that has not been milked by its owner in days or more than that, so the milk accumulates in its udder to impress the purchaser. This is a type of deceit and misrepresentation.
حَدَّثَنَا هَنَّادٌ، حَدَّثَنَا أَبُو الأَحْوَصِ، عَنْ سِمَاكٍ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ، أَنَّ النَّبِيَّ صلى الله عليه وسلم قَالَ لاَ تَسْتَقْبِلُوا السُّوقَ وَلاَ تُحَفِّلُوا وَلاَ يُنَفِّقْ بَعْضُكُمْ لِبَعْضٍ . قَالَ أَبُو عِيسَى وَفِي الْبَابِ عَنِ ابْنِ مَسْعُودٍ وَأَبِي هُرَيْرَةَ . وَحَدِيثُ ابْنِ عَبَّاسٍ حَدِيثٌ حَسَنٌ صَحِيحٌ . وَالْعَمَلُ عَلَى هَذَا عِنْدَ أَهْلِ الْعِلْمِ كَرِهُوا بَيْعَ الْمُحَفَّلَةِ وَهِيَ الْمُصَرَّاةُ لاَ يَحْلُبُهَا صَاحِبُهَا أَيَّامًا أَوْ نَحْوَ ذَلِكَ لِيَجْتَمِعَ اللَّبَنُ فِي ضَرْعِهَا فَيَغْتَرَّ بِهَا الْمُشْتَرِي . وَهَذَا ضَرْبٌ مِنَ الْخَدِيعَةِ وَالْغَرَرِ .
Tirmizi
The Book on Business • Hadith 1277