حَدَّثَنَا عَبْدُ الرَّحْمَنِ حَدَّثَنَا مَالِكٌ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ أَنَّ النَّبِيَّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ نَهَى عَنْ تَلَقِّي السِّلَعِ حَتَّى يُهْبَطَ بِهَا الْأَسْوَاقُ وَنَهَى عَنْ النَّجْشِ وَقَالَ لَا يَبِعْ بَعْضُكُمْ عَلَى بَيْعِ بَعْضٍ وَكَانَ إِذَا عَجَّلَ بِهِ السَّيْرُ جَمَعَ بَيْنَ الْمَغْرِبِ وَالْعِشَاءِ
مسند امام احمد بن حنبل · Hadith 4531
It was narrated from Ibn "Umar that the Prophet (PBUH) forbade intercepting goods until they had been unloaded in the marketplace, and he forbade artificially inflating prices, and he said: "Do not undersell one another.” And if he was in a hurry whilst travelling, he would put Maghrib and 'Isha' together.
Sanad
حَدَّثَنَا عَبْدُ الرَّحْمَنِ حَدَّثَنَا مَالِكٌ عَنْ نَافِعٍ عَنِ ابْنِ عُمَرَ