All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.
We ask Allaah to make us firm and steadfast on His religion until the Day we meet Him.
We recommend that you treat your family, especially your parents, in a good manner, and that you strive to show them the virtues of Islam through your good conduct and good morals and by showing patience over the harm that you may encounter from their side. In fact, Islam has enjoined kindness and dutifulness to parents even if they are non-Muslims. Allaah says (what means): {And We have enjoined upon man [care] for his parents. His mother carried him, [increasing her] in weakness upon weakness, and his weaning is in two years. Be grateful to Me and to your parents; to Me is the [final] destination. But if they endeavor to make you associate with Me that of which you have no knowledge, do not obey them but accompany them in [this] world with appropriate kindness.} [Quran 31:14-15]
Moreover, Asmaa' bint Abu Bakr said: “My mother came to visit me while she was an idolater at the time of the Prophet so I asked him [the Prophet]: “My mother has come desiring my kind treatment. Shall I keep ties with her? He, sallallaahu ‘alayhi wa sallam, said: “Yes, be dutiful to your mother.” [Al-Bukhari and Muslim]
On the other hand, a Muslim's religion is the most precious thing that he has. Therefore, the Prophet, sallallaahu ‘alayhi wa sallam, and his Companions sacrificed their property and their homelands and emigrated in order to save their religion. As a result, Allaah praised them saying (what means): {For the poor emigrants who were expelled from their homes and their properties, seeking bounty from Allaah and [His] approval and supporting Allaah and His Messenger, [there is also a share]. Those are the truthful.} [Quran 59:8]
Hence, you should stay firm on the truth and do not react to any pressure or provocations. You should know that it is normal to find some trouble and harassment from your father as you have chosen a path that is different from the falsehood that he believes, and Allaah, The Almighty, may test the believer so as to make evident who is truthful and who is a liar. Allaah says (what means): {Do the people think that they will be left to say, "We believe" and they will not be tried? But We have certainly tried those before them, Moreover, Allaah, The Exalted, may test make evident those who are truthful, and He will surely make evident the liars.} [Quran 29:2-3]
Therefore, we advise you to be patient and respond to bad deeds with good deeds, as the outcome of this is good. Allaah says (what means): {And not equal are the good deed and the bad. Repel [evil] by that [deed] which is better; and thereupon the one whom between you and him is enmity [will become] as though he was a devoted friend.} [Quran 41:34]
Ibn Katheer said (about the interpretation of the above verse) in his Tafseer (interpretation of the Quran): “That is to say that if you do good to someone who mistreats you, then this good that you do to him will lead him to have a good attitude towards you, love you, and be compassionate with you until he becomes like an intimate friend to you, who is sympathetic and kind to you.” [End of quote]
For more benefit, please refer to Fataawa 92413, 123574, 83911 and 85180.
Hence, if arguing with your father about his false beliefs may cause you such harassment, and perhaps you may even be subject to trials concerning your religion because of it, then you should not do so.
On another note, the scholars have stated that it is not an obligation to seek the permission of one's parents to travel if one does not fear potential harm in that travel, even if one's parents are Muslims. So, with even more reason, the same ruling applies to you since your father wants to prevent you from travelling in order to test your faith. Therefore, it is permissible for you to travel without his permission. For more benefit, please refer to Fatwa 84942.
Dear brother, you are an adult, and we believe that in your country you have laws which guarantee you the freedom of religion, and which prevent your father from oppressing you.
If you are able to get married, then you should take the initiative to marry and look for a Muslim woman who would help you maintain your religion. By doing so, you may be independent of your parents and live with your own family. Also, you should be keen on going to Islamic centers and seeking the help of your Muslim brothers there and consulting them about any action you want to undertake.
For more information on evidence that Islam is the true religion, please refer to Fataawa 86091, 88906 and 173389.
Also, for more information on the falsehood of Christianity and the contradictions in the Bible, please refer to Fataawa 8210, 10326 and 90449.
May Allaah guide you and make you firm on the truth.
Allaah Knows best.