Is it permissible for someone who is pressed for time for prayer and is afflicted by the need to urinate or defecate to enter the restroom, knowing that the prayer time will expire as a result? And would he be sinful for delaying the prayer until its very end in this situation? And is his prayer considered to have been performed within its time if he entered the restroom due to an excuse?

Performing prayer at any part of its time is permissible, but delaying it misses the virtue of performing it at the beginning of its time. This is what is known as the "extended obligation" (al-wājib al-muwassaʿ). Prayer is prohibited when one is suppressing the two impurities (feces and urine). If time is short and the person is suppressing the two impurities, the majority of scholars hold that one should pray despite suppressing them, in order to preserve the sanctity of the prayer time. However, some Shafi'is, a view chosen by Sheikh Al-Uthaymeen, believe that one should relieve oneself even if the prayer time expires, in order to achieve devotion (khushūʿ), especially if the suppression is severe. In this case, the prayer would be a make-up (qaḍāʾ) rather than a performance within its time (adāʾ), and the person would be excused and not sinful.