Some have thought that what is meant is a prostration on its own, but this is mistaken. No scholar has held that catching the prayer depends on catching a single prostration on its own.

Rather, scholars hold three opinions concerning what is required to catch the Friday prayer and the congregational prayer. The soundest is that one has not caught either unless one catches a rak‘ah; merely joining with the opening takbīr does not count as catching the congregational prayer. It is widely reported from the Companions that whoever catches less than one rak‘ah of the Friday prayer must pray four rak‘ahs.

It is authentically reported that the Prophet, may Allah bless him and grant him peace, said:

“Whoever catches one rak‘ah of the prayer has caught the prayer.”

Accordingly, if a traveller catches one rak‘ah behind a resident imam, should he pray the full prayer or shorten it? There are two opinions on this.

The point here is that the word sajdah (prostration) means a rak‘ah, for prayer may be referred to by its constituent parts: standing, sitting, bowing, prostration, glorification of Allah, and recitation of the Quran.

Even more objectionable is the practice of some people who perform a single prostration on its own after the salutation ending the prayer. This is an innovation, and no imam is reported to have recommended it. Acts of worship are founded on revealed law and adherence to it, not on whims and innovation. Islam rests on two foundations: that we worship Allah alone, and that we worship Him as He has prescribed through His Messenger, may Allah bless him and grant him peace—not according to whims and innovations.