The Messenger of Allah ﷺ said, "A Muslim must not make an offer to buy something when his brother has already made an offer for it."
أن رسول الله ﷺ قال: لا يسم المسلم على سوم أخيه.
Muslim narrated it in "The Book of Sales" (1515:9) via Ismail bin Jafar, from Ala, from his father, from Abu Hurairah.The meaning of the hadith is that the owner of the merchandise and its buyer agree on the sale, but have not yet concluded the contract, and then another person says to the seller, "I will buy it for such and such." This is the outbidding that is not permissible. As for bidding on merchandise that is being sold to the highest bidder, this is not forbidden.