Filling the gap in the rows while praying in congregation
Narrated Ayesha may Allah be pleased with her that the Messenger of Allah Peace be upon him said:
«من سدَّ فُرجةً بنى الله له بيتاً في الجنة، ورفعه بها درجةً.»
“Whosever fills the gap (in rows in the prayer), Allah builds for him a house in Paradise and raises his rank”
Al-Albaani: Its Isnaad Is Saheeh li Ghairihi In Saheeh al Targheeb