The wisdom behind the prescription of zakat al-fitr and its amount in the sa' and the kilogram

Question : What is the wisdom behind its prescription? And what is its amount in the sa' and in the kilogram?

Answer : The wisdom behind its prescription is what the Prophet (peace and blessings be upon him) mentioned: that it is a purification for the fasting person from idle talk and obscenity, and food for the poor. So it has two benefits: a benefit for the one who pays it, and a benefit for the one to whom it is paid. As for its benefit for the payer, it purifies his fasting from idle talk and obscenity. As for its benefit for the recipient, it is food for him, which suffices him from asking on that day and on the days of the festival. The first benefit is absent in the case of a child for whom the zakah is paid, because he was not fasting. But the second benefit is not lost, which is that it is food for the poor. For this reason, the Prophet (peace and blessings be upon him and his family) made it obligatory upon the Muslims: their young and their old, their free and their slaves. As that came in the hadith of 'Abdullah ibn 'Umar (may Allah be pleased with them both).
As for its amount, it is a sa' by the sa' of the Prophet (peace and blessings be upon him). And the sa' of the Prophet (peace and blessings be upon him) is less than the sa' in use here by about one-fifth. That is, for example, if our sa' is one hundred, then the sa' of the Prophet (peace and blessings be upon him) is eighty, which is approximately two kilograms and forty grams.
But if a person exercises caution and pays out three kilograms or two and a half kilograms, that is good. Whatever exceeds the obligatory amount becomes voluntary charity. Yes.