من لا يحضره الفقيه, volume 3, page 38

Hadith.3280 - It is narrated from Abdullah ibn Abi Ya'fur, who said: I asked Abu Abdullah (as): "By what means is the righteousness ('Adalah) of a man among the Muslims recognized, so that his testimony may be accepted for or against them?" Imam (as) replied: "It is recognized by his modesty and chastity, by his restraint over his stomach, private parts, hands, and tongue, and by his avoidance of major sins for which Allah (swt), the Mighty and Majestic, has threatened punishment in Hell. These sins include: drinking alcohol, fornication, usury, disobedience to parents, fleeing from battle, and other similar acts. The sign of all this is that he covers his faults and defects, making it impermissible for Muslims to investigate or expose his errors and shortcomings. It becomes obligatory upon them to testify to his righteousness and exhibit his piety among people. Additionally, he must be diligent in observing the five daily prayers, maintaining their times, and attending congregational prayers with the Muslims. He should not miss the congregation at the mosque except for a valid excuse. If he remains steadfast in attending his place of prayer for the five daily prayers, and when asked about him in his community or neighborhood, people say: 'We have seen nothing but good from him. He is regular in prayers, punctual in observing their times, and consistently present at his place of prayer,' then this confirms his testimony and establishes his righteousness among Muslims. This is because prayer serves as a covering and an expiation for sins. It is not possible to testify to a man's observance of prayer unless he attends his place of worship and maintains congregation with the Muslims. Indeed, congregation and assembly for prayer were instituted so that those who pray may be distinguished from those who do not, and those who guard the times of prayer from those who neglect them. Without this, no one could testify to another's piety. Whoever does not pray has no righteousness among the Muslims. The Messenger of Allah (swt) (peace be upon him and his family) even intended to burn the houses of those who abandoned congregational prayer, despite some of them praying at home. This was not accepted from them. How then can the testimony or righteousness of someone be accepted when Allah (swt), the Mighty and Majestic, and His Messenger (peace be upon him and his family) had judged that such a person deserves to be burned in his house during the daytime? The Messenger of Allah (swt) (peace be upon him and his family) used to say: 'There is no prayer for the one who does not pray in the mosque with the Muslims, except due to a valid excuse.'"

Translation: Bab Ul Qaim Publications — attributed by Thaqalayn·The Arabic above is the original.