Al-Qurtubi reported: It reached Umar ibn Abdul Aziz, may Allah have mercy on him, that his son had purchased a ring for a thousand coins, so he wrote to him saying, “Indeed, I have heard that you purchased a ring for a thousand coins, so sell it and feed a thousand starving people and buy a ring of iron for one coin. Write over it, ‘May Allah have mercy on a man who knows his place.’”
Source: Tafsīr al-Qurṭubī 16:14
عن القرطبي بَلَغَ عُمَرَ بْنَ عَبْدِ الْعَزِيزِ رحمه الله أَنَّ ابْنَهُ اشْتَرَى خَاتَمًا بِأَلْفِ دِرْهَمٍ فَكَتَبَ إِلَيْهِ إِنَّهُ بَلَغَنِي أَنَّكَ اشْتَرَيْتَ خَاتَمًا بِأَلْفِ دِرْهَمٍ فَبِعْهُ وَأَطْعِمْ مِنْهُ أَلْفَ جَائِعٍ وَاشْتَرِ خَاتَمًا مِنْ حَدِيدٍ بِدِرْهَمٍ وَاكْتُبْ عَلَيْهِ رَحِمَ اللَّهُ امْرَأً عَرَفَ قَدْرَ نَفْسِهِ
16:14 الجامع لأحكام القرآن