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!'"
Abu'l-'Aliyya said, "We were ordered to finish off things for the
servant and to measure and count because we did not want to allow them
to accustom themselves to bad habits nor for anyone to think evil of us."