Yazid ibn 'Abdullah said, "'Abdullah ibn 'Umar sent a slave of his with some gold - or silver - and he changed it and deferred the exchange (i.e. he changed gold into silver or vice versa and did not take the money straightaway. This is haram.) Then he went back to Ibn 'Umar who gave him a painful beating. He said, 'Go and take what is mine and do not exchange it!'"