Assalamu alaykum. Do we have the right to call this person a brother in Islam due to his arrogance as seen in the following story?There is a brother who did not practiced Islam at a young age and who came to America when he was 18 years old in order to receive an education. When he came to America, he witnessed many things and began to drink, smoke, and so on. At some point in his life, he was working with a Muslim, his boss, who took care of him when he went through a financial crisis. This man thought that the brother was a Muslim, but the brother was not practicing the religion at this point of his life. The boss would pray and always invite the brother to pray along. The brother would pray out of shyness, and it came to the point where the Muslim decided to take him to the masjid for every Friday prayer. From this experience, he was slowly being exposed to Islam. Then, later on, Allaah guided him. He experienced a lot of things, and Allaah blessed him with a family and allowed them to move to Saudi Arabia. When the brother came to Saudi Arabia, he became active as a caller to Islam. Years passed by, and then this brother encountered an individual who was lost in the religion, so he aided him, and they kept in touch for a long time. However, conflicts occurred between them, and this caused the brother to grow arrogant. He began speaking of Allaah without knowledge and wronged the individual. Allaah gave the individual a test to see what they would do. He passed the test by putting his faith in Allaah. Allaah gave the brother a test by allowing the individual to become ill. When the brother received a message from a third party who spoke on behalf of him, he did not answer. When the individual reached out to him to explain what had occurred, he did not answer and blocked his email.After this, Allaah began to make things easy for the individual and gave him many signs to forget about this brother.

All perfect praise be to Allah, The Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.

The bond of brotherhood remains intact as long as this person is a Muslim who testifies that none is worthy of worship but Allah and that Muhammad is the Messenger of Allah, and as long as he has not committed any act of disbelief that takes him out of the fold of Islam. Allah, The Exalted, says (what means): {The believers are but brothers.} [Quran 49:10] The verse described them as brothers despite what was mentioned earlier in the same context; that they were fighting among themselves.

At-Taaher ibn ‘Aashoor wrote, "This verse is strong evidence for the establishment of the obligation of brotherhood among Muslims." [At-Tahreer wa At-Tanweer]

Ibn ‘Umar, may Allah be pleased with them, narrated that the Prophet, sallallahu ‘alayhi wa sallam, said, "A Muslim is a brother to a Muslim..." [Al-Bukhari and Muslim]

Moreover, Anas ibn Maalik, may Allah be pleased with him, reported that the Prophet, sallallahu ‘alayhi wa sallam, said, "Whoever prays like us and faces our Qiblah and eats our Zabeehah (halaal/lawful animals) is a Muslim and is under the protection of Allah and His Messenger. So do not betray Allah by betraying those who are under His protection." [Al-Bukhari and Muslim]

If this person makes a mistake, falls short in his religious duties and obligations, or does an immoral act that is unbecoming of a devout Muslim, then he should kindly be advised in this regard. Tameem Ad-Daari, may Allah be pleased with him, reported that the Prophet, sallallahu ‘alayhi wa sallam, said, "The religion is (built on sincere) advice." People listening asked, "To whom?" The Prophet, sallallahu ‘alayhi wa sallam, replied, "To Allah, to His Book, to His Messenger, to the leaders of the Muslims, and to the common folk." [Muslim]

Allah knows best.