Ali ibn Ibrahim, from al-Nawfali, from al-Sakuni, from Abu Ja'far, from his forefathers (AS), that Ali (AS) used to say: To meet one's brethren is a mighty spoil. (Musadaqat al-Ikhwan, vol. 1, p. 34)
The Commander of the Faithful (AS) said: To meet one's brethren, even if they be few, is a great gain.
From al-Fadl ibn Abi Qurra, from Ja'far, from his father (AS), who said: The Commander of the Faithful (AS) used to say from the pulpit of Kufa: O company of Muslims, let the Muslim take the Muslim as his brother, and let him never take as brother the corrupt, nor the fool, nor the liar. For the corrupt man makes his own conduct seem fair to you and urges you to do the like, and he will help you neither in the affair of your religion nor of your world; his coming in upon you and his going out from you are a disgrace to you. As for the fool, he obeys no guide and is unable to turn evil away from you, and often, when he means to benefit you, he harms you. As for the liar, he stirs up enmity against you, plants rancour toward you in men's breasts, divulges your secret, repeats your words, and carries people's talk from one to another. (Musadaqat al-Ikhwan, vol. 1, p. 78)
The Commander of the Faithful (AS) said: O Muslims! Let the believer befriend the believer, and not the sinner, nor the fool, nor the liar. For the sinner makes sin seem fair in your eyes and urges you to do as he does, and he will not help you in the affairs of religion or of the world. To come and go with such a person is itself a disgrace. As for the fool, he follows no one's guidance and cannot ward off evil from you, and at times when he means to bring you some benefit he does you harm. As for the liar, he stirs up enmity for you, plants hatred of you in people's hearts, discloses your secret, repeats what you have said, and carries talk this way and that.