Riyad as-Salihin (The Meadows of the Righteous)
by Imam Nawawi
What is meant by burying it is to cover it with earth when the floor of the mosque consists of dirt, sand or the like. Abu'l-Mahasin ar-Ruyani, one of our companions, said in his book, al-Bahr, "It is said that what is meant by 'burying it' is to remove it from the mosque. If the mosque is paved or whitewashed and he rubs it with his shoe or something else as many ignorant people do, that is not burying it. It is increasing the error and the amount of filth in the mosque. After that the person who did that should wipe it with a cloth or his hand or something else or wash it,"
1695. Anas reported that the Messenger of Allah, may Allah bless him and grant him peace, said, "These mosques are not a suitable place for any of this urine or filth. They are for remembrance of Allah Almighty and reciting the Qur'an," or as the Messenger of Allah said. [Muslim]