—meaning that he should pray them quickly so he can resume listening to the sermon.

Some scholars have concluded from this ḥadith that the two-rakʿah salutation of the mosque—taḥiyyat al-masjid—is obligatory. The Messenger of Allah ﷺ ordered the man to perform it even though this kept him from hearing the Friday sermon, and listening to the sermon is itself obligatory. One is not excused from an obligation except by something that is even more obligatory. Hence a number of jurists hold that if a person enters the mosque already in a state of wuḍūʾ, sits down, and does not pray, he incurs sin.

We say that such a person is indeed disobedient to the Messenger of Allah ﷺ. There is no doubt that when someone comes in, sits, and he is ritually pure, he is defying the Prophet’s words: “Let him not sit until he has prayed two rakʿahs.”

Among the rulings that pertain to mosques is that buying and selling inside them is forbidden, whether the sum involved is large or small. Do not sell anything for even a single qirsh, for that is unlawful and the transaction is invalid: the price does not lawfully become the seller’s, nor does the merchandise become the buyer’s. Each party must return to the other whatever he received, however insignificant.

This applies even to a simple request such as, “Brother, do you have such-and-such an item?” “Yes.” “Then send me so-and-so of it,” or, “Do you have rice?” “Yes.” “Send us one sack.” If this exchange occurs in the mosque, it is prohibited because it constitutes buying and selling.

Accordingly, commercial transactions of any sort are not permissible in the mosque. Even if a man has 10 riyals and says to another, “I have 10; give me two five-riyal notes in exchange,” it is not allowed.