Al-Kāfi - Volume 3 > Preparing Lahad and the Materials Needed (Ch. 64 is best explained by fatwa.)
Hadith #2

2ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ أَبِيهِ عَنْ صَالِحِ بْنِ السِّنْدِيِّ عَنْ جَعْفَرِ بْنِ بَشِيرٍ عَنْ يَحْيَى بْنِ أَبِي الْعَلاَءِ عَنْ أَبِي عَبْدِ الله (عَلَيْهِ الْسَّلام) قَالَ أَلْقَى شُقْرَانُ مَوْلَى رَسُولِ الله (صلّى اللهُ عَلَيْهِ وَآلِه) فِي قَبْرِهِ الْقَطِيفَةَ.

2. Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from Ali ibn al-Hakam from Husayn ibn ‘Uthman from ibn Muskan from Aban ibn Taghlib who has said the following: “I once heard abu ‘Abd Allah, ‘Alayhi al-Salam, say, ‘Ali, ‘Alayhi al-Salam, placed bricks on the grave of the Holy prophet.’ I then asked, ‘If one places tiles on the grave is it harmful to the deceased?’ He (the Imam) said, ‘No, it is not harmful.’”