بُلُوغُ الْمَرَامِ
Bulugh al-Maram 804
Business Transactions
وَعَنْهُ قَالَ: { نَهَى - صلى الله عليه وسلم -عَنِ النَّجْشِ } مُتَّفَقٌ عَلَيْهِ [1] .
Narrated [Ibn 'Umar (RA)]: Allah's Messenger (ﷺ) forbade bidding against one another (to raise the price). [Agreed upon].
Sunnah.com reference: Book 7, Hadith 29