It was narrated that Ayman bin Umm Ayman who attributed it to the Prophet ﷺ said:
"The (hand of) a thief is not to be cut off except for the price of a shield, and in those days the price of a shield was a Dinar."
أَخْبَرَنَا عَلِيُّ بْنُ حُجْرٍ، قَالَ أَنْبَأَنَا شَرِيكٌ، عَنْ مَنْصُورٍ، عَنْ عَطَاءٍ، وَمُجَاهِدٍ، عَنْ أَيْمَنَ بْنِ أُمِّ أَيْمَنَ، يَرْفَعُهُ قَالَ " لاَ تُقْطَعُ الْيَدُ إِلاَّ فِي ثَمَنِ الْمِجَنِّ " . وَثَمَنُهُ يَوْمَئِذٍ دِينَارٌ .
• Sunan an-Nasa'i, 4948
• Sunan an-Nasa'i, Vol. 5, Book of Cutting off the Hand of the Thief, Hadith 4951
• Sunan an-Nasa'i, Book of Cutting off the Hand of the Thief, Hadith 4951