B19 · باب أهلية الآدمي لوجوب الحقوق له وعليه · Legal capacity: being able to owe, and being able to perform (v2/332–353)

In short

This chapter asks who can owe duties and who can perform them [Overview]. Owing needs a dhimma (fitness to bear duties), which only humans have [B19.01]. Limited capacity makes acts valid; complete capacity makes them owed [B19.03]. A child's dealings are judged by benefit and harm [B19.04].

A discerning child's faith is valid, yet no worship is owed by him before adulthood; his prayer is valid, but his zakāt is not, since financial worship needs complete capacity [B19.03].

In plain words: What makes a person able to owe anything at all? Sarakhsī says capacity for obligation exists only with a dhimma (a fitness to be the seat of obligations), which only humans have. It is the covenant God took from them (Q 7:172). A second capacity, for performance, is complete or limited; B19.03 explains it. The unborn child, part of its mother yet with its own life, has a dhimma only for rights in its favour.
Example: The unborn can receive freedom, inheritance, descent and a bequest, but owes nothing. Once born, it owes damages if it rolls onto someone's property.
Deeper: v1 B19.01

In plain words: Does a newborn already owe prayer and fasting, only excused from them? ⚑ Sarakhsī reports two views among the Ḥanafī shaykhs and rejects both. The first overshoots: God's rights are owed from birth and drop only to spare hardship. The second falls short: nothing is owed until sound-minded adulthood. His middle way: after a cause and a seat (the dhimma), an obligation exists only where the person is fit to perform it by choice. So a child without reason owes no faith and no pure worship. Property rights, such as damages and maintenance, are owed, and the guardian pays them.
Example: A boy who comes of age in the middle of Ramaḍān owes no make-up for the days that passed.
Who disagrees: ⚑ Sarakhsī's teacher al-Ḥalwānī held that faith is owed by a discerning child, since he can perform it. Sarakhsī holds the soundest view is that it is not owed before adulthood. If he believes, it is an obligation performed, like a traveller's Jumuʿa (not owed by him, yet valid if he prays it).
Deeper: v1 B19.02

In plain words: Can a child's acts of worship count? Sarakhsī distinguishes limited capacity, the root of reason with bodily strength, as in a discerning child, from complete capacity, reason and body both complete. Limited capacity makes an act valid; complete capacity makes it owed. The Law ties completeness to its sign, sound-minded adulthood. So a discerning child's faith is valid, here and hereafter. His prayer and fast are valid, since they are pure benefit. His zakāt is not, since financial worship harms his property, so even its validity needs complete capacity. None of them is owed.
Example: A child prays early in the time, then comes of age before it ends. For the Ḥanafīs that prayer is not the obligatory one, since it came before the Law addressed him with the duty; the opponent, whom Sarakhsī does not name here, counts it.
Who disagrees: ⚑ On a discerning child's apostasy, Abū Yūsuf says it does not count in worldly rulings, being pure harm. Abū Ḥanīfa and Muḥammad say it counts, as his faith does; but he is not killed, since killing belongs to fighting, which does not exist before adulthood.
Deeper: v1 B19.03

In plain words: Which of a child's dealings count? Sarakhsī sorts them by benefit and harm. Acts of pure benefit, like accepting a gift or earning a wage, are valid from a discerning child by himself. Acts of pure harm, like giving gifts or freeing a slave, are not valid, whether by him or by his guardian. Mixed dealings, like sale and purchase, are valid by the guardian or with his permission, which removes the feared harm.
Example: A discerning child's bequest is void, and so is his tadbīr (freeing a slave to take effect at his own death), since both are pure harm.
Who disagrees: ⚑ On a discerning child's safe-conduct to the enemy, Muḥammad says it is valid, even if he has not been permitted to fight. It is pure benefit to him, rests on his speech, and binds no one for good, since it can be withdrawn. Abū Ḥanīfa and Abū Yūsuf say it is not valid, since until withdrawn it binds others to stop fighting, while he himself cannot undertake fighting.
Deeper: v1 B19.04