The evidence for this is as follows:

1. The Prophet ﷺ said: “Whoever reaches something before any other Muslim has reached it has the greater right to it.” (1)

2. He ﷺ forbade a man from making his brother get up and then sitting in his place. (2)

The first hadith establishes the prior right, while the second establishes the prohibition of making someone else get up in order to sit in his place.

3. Such conduct creates enmity and resentment among those praying, and this runs contrary to the purpose of congregational prayer. For one of the aims of the congregation is harmony and mutual affection. If someone makes another get up—especially in front of people—there is no doubt that this will hurt him and cause him to harbor rancor toward the man who made him rise.

EXCEPT WHEN SOMEONE SENDS A COMPANION AHEAD TO SIT IN A PLACE AND HOLD IT FOR HIM.

His statement, “Except when someone sends a companion ahead to sit in a place and hold it for him,” means: except in the case of a person who sends a companion ahead to occupy a place for him and keep it for him. For example, he may say to someone: “So-and-so, I have some work which will not be finished until the imam arrives, so go and sit in a place for me in the first row.” If he does so and sits in the first row, then the man may make him get up, because the person who is made to rise is acting as his agent and representative.

The apparent meaning of the author’s words is that this is permissible: a person may appoint someone else to sit in a virtuous place while he remains behind until he has finished his needs, and then proceeds to the mosque.