Umm Bujaid - and she was one of those who gave the pledge to the Prophet - she said to the Messenger of Allah: "There is a needy person who stands outside my door, but I cannot find anything to give to him." So the Messenger of Allah said to her: "If you do not find anything to give him except a burnt trotter then hand it over to him."  

عَنْ جَدَّتِهِ أُمِّ بُجَيْدٍ وَكَانَتْ مِمَّنْ بَايَعَ رَسُولَ اللَّهِ ﷺ أَنَّهَا قَالَتْ يَا رَسُولَ اللَّهِ إِنَّ الْمِسْكِينَ لَيَقُومُ عَلَى بَابِي فَمَا أَجِدُ لَهُ شَيْئًا أُعْطِيهِ إِيَّاهُ فَقَالَ لَهَا رَسُولُ اللَّهِ ﷺ إِنْ لَمْ تَجِدِي شَيْئًا تُعْطِينَهُ إِيَّاهُ إِلاَّ ظِلْفًا مُحْرَقًا فَادْفَعِيهِ إِلَيْهِ فِي يَدِهِ قَالَ وَفِي الْبَابِ عَنْ عَلِيٍّ وَحُسَيْنِ بْنِ عَلِيٍّ وَأَبِي هُرَيْرَةَ وَأَبِي أُمَامَةَ