The Holy Prophet [s] said: "Verily, when one of His servants establishes a prayer in congregation and asks Him something which He does not grant, Allah will be ashamed until He fulfils it."
Bihar-ul-Anwar, vol. 88, p. 4
Imam Ali ibn Musa al-Ridha, the eighth Imam, [a] said: "The excellence of the congregational prayer, comparing with solitary prayer, is one rak'at to two thousand rak'ats."
Bihar-ul-Anwar, vol. 88, p. 4 & Wasa'il-ush Shi'ah, vol. 8, p. 290
The Holy Prophet [s] said: "One prayer of a man in congregation is worthier than his forty years of prayers at home (alone)."
Mustadrak-ul-Wasa'il, vol. 6, p. 446
The Holy Prophet [s] said: "The rows of my followers in the congregational prayer on the earth are like the rows of angels in the sky; and a rak'at of prayer in congregation is equivalent with twenty-four rak'ats, and every rak'at with Allah, Almighty and Glorious, is more beloved than forty years of worship. Therefore, on the Day of Justice, when Allah gathers all human beings from the beginning to the end for Reckoning, there will be no believer who has attended the congregational prayer but for whom Allah will decrease the grievousness of the Day of Reckoning and after that the one will be told to enter Heaven.
Bihar-uI-Anwar, vol. 88, p. 6
Once a blind man came to the Holy Prophet [s] and said that there was not anybody to take him to the mosque to attend the congregational prayer with him [s] when he heard the prayer call. Then the Holy Prophet [s] said: Stretch a thread from your house unto the mosque and attend the congregational prayer."
At-Tahthib, vol. 3, p. 266
Imam Baqir [a] said: "The person who abandons the congregation (of prayer) without having an excuse but only for unwillingness, and in order to avoid attending the folk of Muslims, there will not be (considered) any prayer for him."
Bihar-ul-Anwar, vol. 88, p. 11
Imam Ridha [a] said: "Certainly the congregational prayer has been decreed in order that the pure Faith in Unity, in Islam, and in worshipping Allah be openly revealed and (publicly) manifested, because, thereby and with its apparency the reason of Allah, Almighty and Glorious, will be completed for the totality of people in the East and West (of the world). (Thus, the reality of Islam will be manifested and known and infidelity and paganism before Islam will be like darkness before light which cannot resist and vanishes at last.) Another reason (for decreeing the congregational prayer) is that those who are far from the truth, the hypocrite, and those who take it light but claim Islam, then they may, willy or nilly, treat accordingly and show Islam from them and try to protect (its laws in the society).
Again, the congregational prayer causes people to know each other which makes it allowed and possible that some of them bear witness for some others about their Islam, wherein there is the means of facility and association for righteous deeds and godly actions which prevents too much disobedience against Allah, Almighty and Glorious."
Bihar-ul-Anwar, vol. 88, p. 12