Hadith 6:976
Abu Usama narrated to us, from Hisham, from al-Hasan and Muhammad, that they both used to dislike sitting [on graves]. And [they used to dislike] walking upon them.
حدثنا أبو أسامة عن هشام عن الحسن ومحمد أنهما كانا يكرهان القعود والمشي عليها