Genesis 23:15-16

15‘Listen to me, sir. The land is worth 400 shekels of silver. But the price is not important, because we are friends. Now bury your dead wife there.’

16Abraham agreed to the price that Ephron had asked for. He weighed the correct amount of silver to give to Ephron. The Hittites there knew that it had been done properly. The weight of 400 shekels agreed with the weights that people used at that time.