Mishkat al-Masabih 4005
‘Umair client of Abul Lahm said:
I was present at Khaibar along with my masters who spoke about me to God's Messenger, telling him that I was a slave. He ordered that I should have a sword girded on me, and I was trailing it.* He then ordered that I should be given some inferior goods. I submitted to him a spell with which I used to treat people who were possessed and he ordered me to reject part of it and retain part. 

*Either because he was a small man, or because he was young.

Tirmidhi and Abu Dawud transmitted it, but the latter's version ended at “goods”.
وَعَنْ عُمَيْرٍ مَوْلَى آبِي اللَّحْمِ قَالَ: شَهِدْتُ خَيْبَر مَعَ ساداتي فَكَلَّمُوا فِي رَسُولِ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَكَلَّمُوهُ أَنِّي مَمْلُوكٌ فَأَمَرَنِي فَقُلِّدْتُ سَيْفًا فَإِذَا أَنَا أَجُرُّهُ فَأَمَرَ لِي بِشَيْءٍ مِنْ خُرْثِيِّ الْمَتَاعِ وَعَرَضْتُ عَلَيْهِ رُقْيَةً كَنْتُ أَرْقِي بِهَا الْمَجَانِينَ فَأَمَرَنِي بِطَرْحِ بَعْضِهَا وَحَبْسِ بَعْضِهَا. رَوَاهُ التِّرْمِذِيُّ وَأَبُو دَاوُدَ إِلَّا أَنَّ رِوَايَتَهُ انتهتْ عِنْد قَوْله: الْمَتَاع