The Messenger of Allah ﷺ passed a man who was selling grain. He asked him: How are you selling? He informed him. Revelation them came down to him saying: "Put your hand into it." So he put his hand into it, and felt that it was damp. The Messenger of Allah ﷺ then said: "He who deceives has nothing to do with us." (Using translation from Abū Dāʾūd 3452)   

أَنَّ النَّبِيَّ ﷺ مَرَّ بِرَجُلٍ يَبِيعُ طَعَامًا فَقَالَ كَيْفَ تَبِيعُ؟ فَأَخْبَرَهُ فَأَوْحَى اللهُ إِلَيْهِ أَنْ أَدْخِلْ يَدَكَ فِيهِ فَأَدْخَلَ يَدَهُ فَإِذَا هُوَ مَبْلُولٌ فَقَالَ لَهُ رَسُولُ اللهِ ﷺ لَيْسَ مِنَّا مَنْ غَشَّ  

What is this? He replied: Messenger of Allah, these have been drenched by rainfall. He (the Holy Prophet) remarked: Why did you not place this (the drenched part of the heap) over other eatables so that the people could see it? He who deceives is not of me (is not my follower). (Using translation from Muslim 102)   

أَنَّ رَسُولَ اللهِ ﷺ مَرَّ عَلَى صُبْرَةٍ مِنْ طَعَامٍ فَأَدْخَلَ يَدَهُ فِيهَا فَنَالَتْ أَصَابِعُهُ بَلَلًا فَقَالَ مَا هَذَا يَا صَاحِبَ الطَّعَامِ؟ قَالَ أَصَابَتْهُ السَّمَاءُ يَا رَسُولَ اللهِ قَالَ أَفَلَا جَعَلْتَهُ فَوْقَ الطَّعَامِ حَتَّى يَرَاهُ النَّاسُ مَنْ غَشَّ فَلَيْسَ مِنِّي  

"I heard the Messenger of Allah ﷺ say: 'The Muslim is the brother of another Muslim, and it is not permissible for a Muslim to sell his brother goods in which there is a defect, without pointing that out to him."' (Using translation from Ibn Mājah 2246)   

سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ الْمُسْلِمُ أَخُو الْمُسْلِمِ وَلَا يَحِلُّ لِمُسْلِمٍ إِنْ بَاعَ مِنْ أَخِيهِ بَيْعًا فِيهِ عَيْبٌ أَنْ لَا يُبَيِّنَهُ لَهُ  

[Machine] Has it been clear to you what is in it? I said, "What is in it is apparent fatness and health." He said, "Did you intend it for meat or did you intend it for a journey?" He said, "I rather intended it for hajj." He said, "Indeed, inside its hoof is a hole." He said, then its owner said, "May Allah rectify your intentions, why would you spoil it for me?" He said, "Indeed, I heard the Messenger of Allah ﷺ saying, 'Whoever sells something, it is not lawful for him until he clarifies what is in it, nor is it lawful for the one who knows that to conceal it.'"  

هَلْ بُيِّنَ لَكَ مَا فِيهَا؟ قُلْتُ وَمَا فِيهَا إِنَّهَا لَسَمِينَةٌ ظَاهِرَةُ الصِّحَّةِ؟ فَقَالَ أَرَدْتَ بِهَا لَحْمًا أَوْ أَرَدْتَ بِهَا سَفَرًا؟ قَالَ قُلْتُ بَلْ أَرَدْتُ عَلَيْهَا الْحَجَّ قَالَ فَإِنَّ بِخُفِّهَا نَقْبًا قَالَ فَقَالَ صَاحِبُهَا أَصْلَحَكَ اللهُ مَا تُرِيدُ إِلَى هَذَا تُفْسِدُ عَلَيَّ؟ قَالَ إِنِّي سَمِعْتُ رَسُولَ اللهِ ﷺ يَقُولُ مَنْ بَاعَ شَيْئًا فَلَا يَحِلُّ لَهُ حَتَّى يُبَيِّنَ مَا فِيهِ وَلَا يَحِلُّ لِمَنْ يَعْلَمُ ذَلِكَ أَنْ لَا يُبَيِّنَهُ