Why is it mentioned to love each other for the sake of Allah? Is it a religious obligation or is there any other aspect to it?

It is the nature of human beings to love others from what one gets from them. For example, one may say ‘so and so gives me so I love him, when they don’t give me I don’t love them anymore’. This is human nature - we tend to love people for what we get from them; whereas true love, the higher love which is pleasing to Allah and for which we get reward is to love our brothers and our sisters only for the sake of Allah. We meet them and separate from them for the sake of Allah. There are no ulterior motives. This means that our brothers and sisters have rights in our wealth, and we help them whenever the opportunity presents itself.

There are a number of rights of brotherhood which the Prophet (ﷺ) spoke of. The rights of brotherhood not only involve giving and sharing of what we have but also protecting one’s honor. When we love somebody for the sake of Allah, we protect their honor, meaning that if people are speaking ill about our brothers and sisters, we stop them and don’t allow them to backbite or slander. We are not silent in times when their honor is being destroyed; rather we are silent about their faults when there is no need to express them. [1] There are some times when we should speak about the faults of our brothers and sisters, for example, in times of marriage. If there are things which are wrong, they should be told or informed about it. [2] This is the question of trust and amanah, where people trust you to give the correct information.

This was the methodology of the Prophet (ﷺ) when Fatima bint Qais asked him about the marriage to Abu Sufyan and Amr ibn ul Aas. Both these people proposed to her. The Prophet (ﷺ) said to her, “Amr ibn ul Aas is known to beat his women and Abu Sufyaan is stingy as he doesn’t share his money.” He then said, “If you really want a good husband then marry Usamah ibn Zaid.”[3] We see that he recommended somebody else. It is also allowed to speak about the others when it comes to business deals, where you ask someone their opinion about a person you plan to enter into a business deal with or make your business partner. You cannot just say that he or she is a good sister or brother because you don’t want to speak something bad about the person. It is your responsibility to protect your brother or sister where they may be harmed by an individual, but there is a time where you must speak. This doesn’t mean you just let loose and discuss everything you dislike about the person, rather speak only about the related information for which the request is made.

Thus, this is what is meant by meeting and parting for the sake of Allah. It also includes advising each other for the sake of Allah:

“Advise each other to truth and advise each other to patience.” [4]

They advise each other to be truthful. Furthermore, they excuse the mistakes of others, and try to have good thoughts about their brothers and sisters. The Prophet (ﷺ) said: “A believer is a mirror of his fellow believer.” [5]

As believers, we should make dua’ for our brothers and sisters in this life as well as after their death because Prophet (ﷺ) said: “The supplication of a brother for his brother in their absence is not rejected by Allah.” [6]

We should also give them the benefit of doubt where the circumstance appears as if they have done something wrong. We should try to find some excuse because it maybe that we have misunderstood, or they misunderstood and did not intend this.

Allah has warned us when he said:

“Indeed some form of doubts is sin.” [7]

The Prophet (ﷺ) said: “Beware of doubts for indeed speaking about doubts is the worst of the most lying form of speech.” [8]

References:

[1] Abu Huraira reported Allah's Apostle (ﷺ) as saying: “The servant (who conceals) the fault of others in this world, Allah would conceal his faults Day of Resurrection.” [Muslim, Book 32, Hadith 6267]

[2] See Commentary on the Forty Hadith of Al-Nawawi, Jamaal al-Din M Zarabozo, 1322

[3] Muslim, Book 9, Hadith 3526

[4] Surah Mai’dah, 5:2

[5] Narrated by Abu Hurayrah, Sunan Abu Dawood, Hadith 4918; classed as hasan by al-Albaani

[6] Muslim, Book 35, Hadith 6588

[7] Surah Hujurat, 49:12

[8] Narrated by Abu Harayrah, Bukhari, Book 8, Volume 80, Hadith 717