A-4.6: How Much One Must Teach One's Children
Shafi'i and colleagues (Allah have mercy on them) say that fathers and mothers must teach their children what will be obligatory for them after puberty. The guardian must teach the child about purification, prayer, fasting, and so forth; and that fornication, sodomy, theft, drinking, lying, slander, and the like are unlawful; and that he acquires moral responsibility at puberty and what this entails. It has been said that this education is merely recommended, but in fact it is obligatory, as the plain content of its scriptural basis (n: mentioned below) shows. Just as it is mandatory for a guardian to wisely manage his charge's property, this is even more important. The merely recommended is what exceeds this, such as teaching him the Koran, Sacred Law, etiquette, and teaching him what he needs to earn a living.
The evidence for the obligation of teaching a young child is the word of Allah Mighty and Majestic,
"O you who believe, protect yourselves and families from a fire" (Koran 66:6).
'Ali ibn Abi Talib (Allah be well pleased with him), Mujahid, and Qatada say it means. "Teach them that with which they can save themselves from hell,"