Praise be to Allah.
Our advice is that the mother or father should from time to time examine their children’s belongings. That is because the Shaytaan may make attractive to them the idea of keeping something haraam that it is not permissible to look at or listen to. This is part of the responsibility that Allah has enjoined upon parents towards their children.
For many sons and daughters, the means of their being guided and their giving up evil things that they are indulging in is the watchfulness of their fathers and mothers, and their taking good care of them. It is easy to put a stop to evil at the beginning, or to warn against bad friends at the beginning, but if it has been going on for a long time, it will be difficult to rescue sons and daughters from this bad company.
In most cases, it will be possible to find out what bad things your sons and daughters have by inspecting their bags, reading their books and getting to know their friends.
How many young men and women have wished that their parents had watched what they were doing and examined their belongings at an early stage, before corruption took a hold of their hearts.
Hence we advise you to do this from time to time, without letting them realize that, lest they take precautions and avoid keeping anything dubious with their stuff.
This watching should be done if the parent sees some indication that his child is starting to go astray. But if it seems that the child is righteous and keeping away from evil things, then neither the parents or anyone else has the right to watch over the child or inspect his personal belongings, because that comes under the heading of suspicion and spying, which Allah has forbidden when He said (interpretation of the meaning):
“O you who believe! Avoid much suspicion; indeed some suspicions are sins. And spy not”
But if the mother or father finds something haraam, then they have to destroy it, and then advise the child in whose possession this evil thing was found.
It was narrated that Abu Sa’eed al-Khudri said: I heard the Messenger of Allah (peace and blessings of Allah be upon him) say: “Whoever among you sees an evil action, let him change it with his hand (by taking action); if he cannot, then with his tongue (by speaking out); and if he cannot, then with his heart (by hating it and feeling that it is wrong), and that is the weakest of faith.”
(Narrated by Muslim, 49).
Imam al-Nawawi said:
With regard to the Prophet’s words “let him change it”, this is a positive command, according to the consensus of the ummah(Muslim community). The Qur’aan, Sunnah and consensus of the ummah all agree that it is obligatory to enjoin what is good and forbid what is evil; this is also part of the sincerity (naseehah) which is the religion.
Moreover, enjoining what is good and forbidding what is evil is fard kafaayah (a communal obligation). If some of the people undertake to do it, the rest are absolved of blame; but if they all fail to do it, then everyone who was able to do it but did not, with no excuse and no fear, is guilty of sin.
But it may become fard ‘ayn (an individual obligation), for example if it is in a place which no one knows but him, or no one can remove it but him, or if he sees his wife, his son or his slave doing something evil, or falling short in doing something good.
Al-Qaadi ‘Iyaad (may Allah have mercy on him) said: This hadeeth (prophetic narration) sets out the principle of changing evil. The one who seeks to change it can do so by whatever means possible, and remove it by word or deeds. So he may break the instruments of falsehood and spill (alcohol) himself or order that this be done, and he can take items seized by force and return them to their owners himself, or he can issue orders that this be done, but he should be gentle with the ignorant, and also with those in positions of power and status, if there is any fear of their evil, because they are more likely to respond to gentleness than harshness.
Sharh Muslim, 2/22-25
And Allah knows best.