Jabir said God’s messenger forbade that graves should be plastered with gypsum, have any writing on them, or be trodden on. Tirmidhi transmitted it.

وَعَنْ جَابِرٍ قَالَ: نَهَى رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ أَن تجصص الْقُبُور وَأَن يكْتب لعيها وَأَن تُوطأ. رَوَاهُ التِّرْمِذِيّ