Hadith 4:181
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
Original Reference: Mishkat al-Masabih 1709