Translation:Shulchan Aruch/Choshen Mishpat/189
Paragraph 1- A sale is not completed with words. If one tells another, what it would take for you to give me this item, and the seller says for such and such amount, and they both agreed and set a price, they both can retract. Even if there were witnesses there and they told the witnesses that they should be witnesses that this party sold and this party bought, it is of no effect until the sale is completed in the appropriate method for the particular item. Real property will be completed with their kinyan, living items with theirs and movable items with theirs. Once the appropriate kinyan for the item has been completed, neither party can retract, even if there were no witnesses on the matter. Even if the parties subsequently waived their rights to each other it would be of no effect. Rather, they must go back and make a kinyan to one another.