The Prophet ﷺ said, "The merit of a man's prayer in congregation over his prayer alone is twenty-five times."
عن النبي ﷺ قال: فضل صلاة الرجل في الجمع على صلاته- يعني وحده- خمسا وعشرين صلاة.
Bazzar narrated it in Kashf Astar (455), Muhammad bin Muthanna and Amr bin Ali told us, they said, Muhammad bin Jafar told us, Shuba told us, from Qatada, from Uqba bin Wassaj, from Abu Ahwas, from Abdullah, and he related it.Tabarani also narrated it in Al-Kabir (10100) through the route of Imam Ahmad, from Muhammad bin Jafar, with the same wording. It is also found in Al-Musnad (4158), but in that chain "Qatada" was dropped between Shuba and Uqba bin Wassaj, making it appear that Shuba narrated directly from Uqba bin Wassaj. This is something unlikely, for Shuba was born in the very year Uqba bin Wassaj died, which was the year eighty-two. Hafiz said in Taqrib, "Uqba bin Wassaj was killed after the year eighty."Ibn Khuzayma graded it sahih (1470), narrating it through the route of Muhammad bin Jafar, from Shuba, from Qatada, from Uqba bin Wassaj, with the same wording.Hammam followed Shuba in narrating this, saying, Qatada informed us, from Murawaq, from Abu Ahwas Jashami, from Ibn Masud, "The Prophet ﷺ used to hold that praying in a group is superior to a man praying alone by twenty-five prayers, each one equal to his prayer."Imam Ahmad narrated it (4159) from Bahz (that is, Ibn Asad Ammi), from Hammam (that is, Ibn Yahya Awdhi), with the same wording. Tabarani also narrated it in Al-Kabir (10099) and in Al-Awsat (2618) through the route of Hammam, with the same wording.Ibn Abu Hatim said in Al-Ilal (1/122), "I asked my father about a hadith narrated by Shuba, from Qatada, from Uqba bin Wassaj, from Abu Ahwas, from Abdullah bin Masud, from the Prophet ﷺ, who said, 'Praying in a group is superior to a man praying alone.' It was also narrated by Hammam and Saeed bin Bashir, from Qatada, from Murawaq Ajli, from Abu Ahwas, from Abdullah, from the Prophet ﷺ. It was also narrated by Aban, from Qatada, from Abu Ahwas, from Ibn Masud, from the Prophet ﷺ. I said to my father, 'Which of these is more accurate?' He said, 'The hadith of Shuba, because he had the stronger memory.'" End of quote.On this subject there are also reports from Abdullah bin Zayd, Suhayb, Zayd bin Thabit, Muaz bin Jabal, Ibn Abbas, Ibn Umar, Abu Hurairah, Abu Darda, Jabir, and Abu Saeed Khudri, among others, though all of these contain points of criticism.