Muhammad bin Yahya bin Abi 'Umar محمد بن يحيى بن أبي عمر العدني · The Book on Business

From Ibn 'Umar, that the Messenger of Allah (ﷺ) said: "Both the buyer and the seller retain the option as long as they have not separated or they give each other than option." He (Nafi') said: "So when Ibn 'Umar purchased something while he was sitting, he would stand to complete the sale."