Is it permissible for a worshipper to begin praying alone behind the Imam if he knows that other worshippers will join him in the row?

The majority of scholars hold that it is disliked for an individual to pray alone behind a row without an excuse. However, the Hanbalis consider the prayer of one who prays a complete rak'ah alone behind a row without an excuse to be invalid. It is permissible to enter ihram behind the row if you know that someone will stand with you. If no one comes, scholars differ on the permissibility of pulling someone from the row; some permit it, while others dislike it. It is preferable not to pull anyone. There is no harm in an individual praying alone behind the row if the row is full; this is considered an excuse.