Prophet Muhammad (pbuh) said:

Among the duties of this love are the following: 1. They must truly love to extend support and assistance to each other and must love good for one another. The Prophet (peace be upon him) said: “None of you believes until he loves for his brother what he loves for himself.” [Sahîh al-Bukhârî(13) and Sahîh Muslim (45)] 2. They must enjoin each another to truth and patience and give each other sincere advice. They must enjoin what is right and the forbid what is wrong and guide each other. They must help one another in carrying out works of righteousness. Allah says: “By time! Surely the human being is at loss. Except for those who have faith and do righteous deeds and exhort one another to truth and exhort one another to patience.” [Sûrah al-`Asr] Allah also says: “The believing men and women are protecting friends of one another. They enjoin what is right and forbid what is wrong.” [Sûrah al-Tawbah: 71] 3. They must engage in the things that cultivate this love, strengthen interpersonal relationships, and facilitate the fulfilling of their duties to one another. The Prophet (peace be upon him) said: “A Muslim has six rights over another Muslim.” They asked: “What are they, O Messenger of Allah?” He said: “When you meet him, greet him with peace. When he invites you, accept his invitation. When he seeks your advice, advise him. When he sneezes and them praises Allah, invoke Allah’s blessings upon him. When he falls ill, visit him. When he dies, follow his funeral.” [Sahîh Muslim (2162)] 4. A Muslim has the right to kind treatment from his fellow Muslim. He should be greeted with a smile and given a pleasant reception. The Prophet (peace be upon him) said: “Do not view any good act as insignificant, even the act of greeting your brother with a smile on your face.” [Sahîh Muslim(2626)] Discord and division should be avoided. Ibn Taymiyah said: “If every time two Muslims disagreed they shunned each another, then there would be no cooperation or brotherhood among Muslims.” 5. They must guide each other to what is good and help each other in acts of obedience. Likewise, they must prevent and discourage one another from falling into sin and iniquity. The Prophet (peace be upon him) said: “One should help his brother whether he is an oppressor or the one being oppressed. If he is an oppressor, forbid him from his oppression and in that way you help him. If he is being oppressed, then come to his aid.” [Sahîh Muslim (2584)] 6. The love between believers completes itself in a most wonderful and genuine manner when the two are away from each other, and each of them in secret prays to Allah for the other. This continues for the living one even after the other has departed from the Earth. The Prophet (peace be upon him) said: “A Muslim’s supplication for his brother in secret is answered. At his head an angel is appointed, and whenever he supplicates for his brother with something good, the angel appointed to him says: ‘Amîn, and likewise for you’.” [Sahîh Muslim (2733)] 7. They must excuse one another’s mistakes and defend each other’s honor, never speaking ill of or deriding one another. They should keep each other’s secrets, advise one another sincerely, and never abuse each other. The Prophet (peace be upon him) said: “It is not permissible for one Muslim to distress a another.” [Sunan Abî Dâwûd (5004) and Musnad Ahmad (23064)]