Here is a nice story from the life and teachings of Srila Bhaktisiddhanta Sarasvati Thakur.
Once, some devotees were sent to establish a preaching center in Bengal. They worked day and night, equipping it as a beautiful temple. When Srila Bhaktisiddhanta Sarasvati arrived to install the Deities, he was very pleased and asked about one brahmacari who had worked hard on the preparations. The disciples told him, "Master, he became entangled with a lady. We rebuked him so much for his behavior that he fled from this place."
Srila Bhaktisiddhanta replied, "I don't want to establish a preaching center here, nor do I want to install the Deities. In this world we spend hundreds of gallons of blood to bring a person out of the clutches of maya. If that person makes some mistake, it will be washed away by his serving Hari, Guru, and Vaisnavas, but you have chastised him and he has gone away. I don't want to make a center here. Search for him and bring him to me; otherwise I will go away."
The anxious disciples began to search for that brahmacari. Madhava Maharaja, who at that time was named Hayagriva Brahmacari, found the errant brahmacari, apologized, and asked him to return.
The brahmacari wept, saying, "I was serving here, in a watch company, but I was not really happy. I wanted to return, but I was thinking, 'How can I show my face?' So I did not return." He at once went running and weeping to Srila Bhaktisiddhanta, thinking him more merciful than Krishna Himself, and all his anarthas were washed away in a moment.
Bhaktisiddhanta told his disciples, "The purport is that we should not criticize anyone, whether a devotee or a worldly person." Then he quoted a sloka:
The Supreme Personality of Godhead said: “One should neither praise nor criticize the conditioned nature and activities of other persons. Rather, one should see this world as simply the combination of material nature and the enjoying souls, all based on the Absolute Truth. Whoever indulges in praising or criticizing the qualities and behavior of others will quickly become deviated from his own best interest by his entanglement in illusory dualities."– Srimad-Bhagavatam (11.28.1-2)
Bhaktisiddhanta continued: "To bring a person from the clutches of maya is very, very hard. If lust or any other attachment is present in that person's heart it will go away very soon, if he is chanting and remembering and listening to Hari-katha. Be very careful. Don't criticize devotees or non-devotees. First look at your own condition, and try to purify yourself. Is there any lust in you? Is there any kutinati (deceit) in you, or not? Be worried for that; don't worry for others. Sri Guru and Lord Sri Krishna are responsible for others. You cannot do anything to help them, so you have no right to criticize."
All Glories to Srila Bhaktisiddhanta Sarasvati Thakur!