The Gemara on today’s daf discusses a variety of situations where a person is limited in his ability to pray. For example, one may not hold phylacteries in his hand or a Torah scroll in his arm and pray, because his concern that the phylacteries or Torah scroll might fall will distract him from his prayer.
Another example is someone who needs to go to the bathroom. The Gemara quotes a baraita that teaches:
One who needs to relieve himself may not pray, and if he prayed, his prayer is an abomination.
Rav Zevid and some say Rav Yehuda said in qualifying this statement:
They only taught this halakha in a case where one cannot restrain himself. But, if he can restrain himself, his prayer is a valid prayer as he is not tarnished by his need to relieve himself.
In this case there are two reasons that he cannot pray. First, he is distracted and unable to concentrate on his prayer; and because one who needs to relieve himself is considered filthy and unfit to pray.
The Gemara continues:
And for how long must he be able to restrain himself? Rav Sheshet said: For as long as it takes to walk one parasang.
The determination of the length of time necessary to walk a parasang is connected to the disagreement with regard to the basic unit of measurement, the time necessary to walk a Talmudic mil. The talmudic mil is a unit of distance related to, but not identical with, the Roman mile, from which it received its name. One mil is equal to 2,000 cubits, 960 m (1,049 yd) according to Avraham Chaim Na’e, or 1,150 m (1,258 yd) according to the Ḥazon Ish. The fundamental problem lies in the method used to determine a person’s regular walking pace. According to the various opinions, the time it takes to walk a parasang is either one hour and twelve minutes or one hour and thirty-six minutes.