Al-Adab Al-Mufrad, Book 9, Hadith 170 (English) ⓘ

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!'"

حَدَّثَنَا أَحْمَدُ بْنُ عِيسَى، قَالَ‏:‏ حَدَّثَنَا عَبْدُ اللهِ بْنُ وَهْبٍ قَالَ‏:‏ أَخْبَرَنِي مَخْرَمَةُ بْنُ بُكَيْرٍ، عَنْ أَبِيهِ قَالَ‏:‏ سَمِعْتُ يَزِيدَ بْنَ عَبْدِ اللهِ بْنِ قُسَيْطٍ قَالَ‏:‏ أَرْسَلَ عَبْدُ اللهِ بْنُ عُمَرَ غُلاَمًا لَهُ بِذَهَبٍ أَوْ بِوَرِقٍ، فَصَرَفَهُ، فَأَنْظَرَ بِالصَّرْفِ، فَرَجَعَ إِلَيْهِ فَجَلَدَهُ جَلْدًا وَجِيعًا وَقَالَ‏:‏ اذْهَبْ، فَخُذِ الَّذِي لِي، وَلاَ تَصْرِفْهُ‏.‏