It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Do not sell over one another."

It is narrated from Sayyiduna Abu Huraira (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Do not meet traders on the way to buy their goods before they reach the market, and none of you should sell over the sale of his brother, and do not practice najsh (artificially inflating prices), and a townsman should not sell on behalf of a villager, and do not collect milk in the udders of camels and goats (i.e., do not withhold milking to deceive buyers). If someone buys such a she-camel or goat, and after milking it comes to know of the situation, then the buyer has the option: if he wishes, he may keep it, or if he wishes, he may return it, and in exchange for the milk, he should give one sa‘ (measure) of dates."

Imam Malik, may Allah have mercy on him, said that regarding the saying of the Messenger of Allah, peace and blessings be upon him: "None of you should sell over the sale of his brother," it means that a person should not make an offer over the offer of another when the seller has already agreed to the first offer, has started weighing his goods, and has begun to declare himself free from defects, or does any other act which shows that the seller has accepted the first offer. But if the seller has not agreed to the first offer and has kept the goods for sale as before, then it is permissible for anyone to make an offer. And if, as soon as one person makes an offer, others are prohibited from making offers, then this would be a loss for the seller.

Malik said: There is no harm in bidding on a commodity that is put up for sale, and more than one person bids on it. He said: And if people were to stop bidding at the first person who bids on it, it would be taken for a price close to falsehood, and something disliked would enter upon the sellers regarding their goods. And the matter has always been thus among us.

It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) forbade najsh (artificially inflating prices). Imam Malik (may Allah have mercy on him) said: And najsh is that a person offers a price higher than the actual value of the goods, not with the intention of buying, but so that another person is deceived and buys it at that price.