He was asked:

“Has the Lawgiver (peace and blessings be upon him) prescribed a fixed distance for shortening the prayer?”

He replied:

The Sunnah is for the traveller to shorten the prayer, offering two rak‘ahs instead of four. This is what the Messenger of Allah (peace and blessings be upon him) and his Companions did on all his journeys. He never offered four rak‘ahs while travelling. The report that “he offered four rak‘ahs while travelling during his lifetime” is a false hadith according to the leading hadith scholars.

Scholars have differed concerning a traveller offering four rak‘ahs. Some maintain that this is impermissible, just as it is impermissible to offer four rak‘ahs for the dawn, Friday, or Eid prayers. Others hold that it is permissible, although the overwhelming majority consider shortening preferable, with only an anomalous dissenting view.

Shortening the prayer requires no specific intention—even if one begins the prayer intending to offer four rak‘ahs—in keeping with the Sunnah of the Messenger of Allah (peace and blessings be upon him).

“When he (peace and blessings be upon him) led the Muslims on the Farewell Pilgrimage, he would lead them in prayers of two rak‘ahs each until he returned.”

He combined the two prayers at ‘Arafah and Muzdalifah, with the Muslims praying behind him. The people of Mecca and others followed him in both combining and shortening the prayers. He did not instruct anyone to form a specific intention either to combine or to shorten them.