وَعَنْهُ قَالَ: «نَهَى صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ عَنِ النَّجْشِ»
The Messenger of Allah (sallallahu alayhi wa sallam) forbade bidding against one another (to raise the price).
Bulugh al-Maram 918, Book 7, Business Transactions, Hadith 29. 1 min read