Sunan Abi Dawud 458

Sahl ibn Tammam ibn Baziʿ narrated to us: ʿUmar ibn Sulaym al-Bahili narrated to us, from Abu al-Walid, who said: I asked Ibn ʿUmar about the gravel in the mosque. He replied: ‘Rain fell on us one night, and by morning the ground was wet. A man would come carrying gravel in his garment and spread it beneath himself.’ When the Messenger of Allah (peace and blessings be upon him) finished the prayer, he said: ‘How good this is!’