I have custody of my son. Is it permissible if I take him with me without his father’s consent while traveling?

It is impermissible for a woman to take any course of action concerning the child under her custody without the permission of the father who is the child’s legal guardian. She cannot for instance travel with the child to a distant country during the custody period because doing so, causes great harm to the father and may not be in the best interest of the child. Al-Kasaani said in Badai’ Al-Sanai’ (98/248, "Even if a mother wishes to take the child to a country other than hers…she is not entitled to do so … .”

And God Almighty knows best.