Discussion of the hadith: “Whoever dies with fasting remaining, his guardian fasts on his behalf,” and of the usul principle: “The narrator is more aware of his narration than others.”

The Shaykh : Here, a question may arise in the mind: How can it be said that no one fasts on behalf of another, when the Messenger of Allah (peace and blessings be upon him) says in the authentic hadith: ? So this seems to contradict what I said earlier!
The answer: The hadith refers to one who dies with a vowed fast remaining, not an obligatory fast. That is, he made a vow upon himself for a fast that Allah (Mighty and Majestic) had not made obligatory upon him, except by his own obligation of this fast upon himself. This is the case in which the guardian of the deceased may fast on his behalf. Where did we take this restriction from?
Here is an issue related to a usul fiqh principle, namely: “The narrator is more aware of his narration than others.” “The narrator” means the narrator of the hadith, “more aware of his narration than others.” This principle, O students of knowledge, if you understand it and it becomes firmly established in your minds, will help you understand some of the disputed issues among scholars correctly. The narrator of the hadith from the Messenger of Allah (peace and blessings be upon him), and indeed the narrator from a Companion of the Messenger of Allah (peace and blessings be upon him), and so on, as you descend until the hadith is classified: the first narrator is the Companion, then the Tabi'i, then the Tabi' al-Tabi'in, then the followers of that Tabi'i, and so on until it is classified. This principle covers all these categories: “The narrator is more aware of his narration than others.” So here we begin with the first narrator. This hadith was narrated by two noble Companions, one of them being Aisha (may Allah be pleased with her), and the other Abdullah ibn Abbas (may Allah be pleased with them both). These two narrators understood the hadith to refer to the fast of a vow. So, “The narrator is more aware of his narration than others.”