It is recommended for him to shorten a four-unit prayer once he has left the built-up area of his town or the tents of his people.

The author’s statement, “It is sunnah for him to shorten a four-unit prayer to two units”: the term sunnah has two usages—one in the terminology of the jurists, and another in the usage of the Companions and the early generations of the ummah.

For the early generations of the ummah and the Companions, sunnah meant the way followed by the Prophet, peace and blessings be upon him, whether it was obligatory or recommended. An example is the statement of Anas ibn Malik, may Allah be pleased with him: “It is from the sunnah that, if a man marries a virgin after a previously married woman, he remains with her for seven days.” (1) This is an obligatory sunnah.

Likewise, when Ibn Abbas, may Allah be pleased with them, was asked about a man who prays four units behind an imam who is resident, but prays two units when he prays alone while travelling, he replied: “That is the sunnah.” (2) That is, it is the obligatory sunnah.

In the terminology of the jurists, however, sunnah refers to that for which its doer is rewarded, while the one who leaves it is not punished.

Thus, the author’s statement, “It is sunnah for him to shorten a four-unit prayer,” uses sunnah in this technical sense: the more correct view, for which one is rewarded, is to shorten a four-unit prayer to two units.

The four-unit prayers are Dhuhr, Asr, and Isha. The evidence for this is found in the Book of Allah, the sunnah of the Messenger, peace and blessings be upon him, and the consensus of the ummah.

As for the Quran, Allah Most High says:

“And when you travel through the land, there is no blame upon you for shortening the prayer, if you fear that those who disbelieve may attack you.”