“Sajl”—pronounced with a fatḥah on the sīn and a silent jīm—denotes a bucket filled with water, and the same meaning applies to a dhanūb.

Explanation
The author—may Allah have mercy on him—included, in the chapter on forbearance, deliberation, and gentleness of his Riyāḍ al-Ṣāliḥīn, the hadith narrated by Abū Hurayrah (may Allah be pleased with him) that a Bedouin once urinated in the mosque.

The term “Bedouin” refers to a desert Arab. Such people generally do not know the rulings of the Sacred Law, for they live out in the desert with their camels or sheep and lack knowledge of Allah’s legislation, just as the Most High says: “The Bedouin are more intense in disbelief and hypocrisy and more likely not to know the limits that Allah has revealed to His Messenger” (Qur’an 9:97). That is, they are more prone to ignorance of the limits Allah sent down because, dwelling in the desert, they are far from people, knowledge, and the Law.

This particular Bedouin entered the mosque and felt the need to relieve himself, so he urinated in one part of it—he stepped aside and did so inside the mosque. The people were about to fall upon him and scold him, but the Prophet ﷺ said to them, “Leave him—let him finish—and pour over his urine a bucketful (sajl) of water or a pail (dhanūb) of water, for you have been sent as facilitators, not as those who impose hardship.” So they left him alone.

When he had finished, they poured a dhanūb—that is, a bucket—of water over the spot; the place became clean and the potential harm was removed. The Prophet ﷺ then called the Bedouin and said to him, “These mosques are not suitable for anything of filth or impurity; they are only for prayer, the recitation of the Qur’an, and proclaiming Allah’s greatness,” or words to that effect.