I am married to a woman who has a son from previous marriage. All the women and men in my wife's family are non-Muslims and all the women and men in the boy's father family are non-Muslims. At the time of my marriage the boy's father was in prison so the boy was living with me and his mother. A few months ago his father came out of prison, and he is asking to have contact with his son and then to have custody of his son. I know for a fact that he is person of extremely bad manners and I cannot trust him to even give him my phone number.My question is: If my wife and I believe that the best interest of the boy and the safety of our family is not to allow contact between the boy and his son until he gets older (he is 8 years old now), are we allowed to do so?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

According to the most correct opinion among Muslim scholars, a son (daughter) must follow in the religion of his/her Muslim parent, so he/she is considered a Muslim. In this vein, the Prophet (Sallallahu Alaihi wa Sallam) said: "His/her parents make him/her a Jew and Christian" . [Reported by Imams Bukhari and Muslim ]
From the above-mentioned Hadith we can deduce an indication to the fact that just as the son/daughter may follow his/her non-Muslim parent, it is more appropriate and with greater reason to follow his/her Muslim parent.
Thus, we say to the inquirer that if this son's mother is a Muslim, then the son is a Muslim. In addition, if it is in your hand, you should not give him to a non-Muslim father, whose morals are very bad.
There is not doubt that the son's interest lies in staying in a Muslim home and good environment, Insha Allah.
But, you should not prevent him from visiting or calling his father since this is the right of fatherhood unless you fear a bad influence on you or the son. Moreover, since the father has bad morals and is not a Muslim, one cannot use such an excuse to cut off the father's relations with his son or to prevent the son from treating his father with kindness and righteousness.
In this issue, we advise you to take what is more beneficial for all of you into consideration. In other words, do not give this good son to his non-Muslim father, nor prevent him from visiting or getting in touch with his father unless you fear his bad influence on the boy's religion or body or any harm to you.
We ask Allah to grant you and us success and steadfastness on the right and good will to do well for this present life and for the Hereafter.
Allah knows best.