What is the reason for reading "عليه" (ʻalayhi) with a dammah over the letter ha (عليهُ) in the verse, "and whoever fulfills that which he has covenanted with Allah – He will surely give him a great reward," contrary to the rules of Arabic grammar?

The letter ha in the word “alayhi” in the verse about the فتح (victory) is read with a kasra (i-vowel) by the majority of reciters. However, Hafs, transmitting from Asim, reads it with a damma (u-vowel). The reason is that the origin of this ha is the detached pronoun “huwa” (هو), which has a damma. However, if it is adjacent to a kasra or a silent ya, it is broken (given a kasra) to harmonize with them. Therefore, the majority of reciters gave it a kasra in consideration of this harmonization, while Hafs gave it a damma in consideration of its origin. An example similar to this is the ha in the word “ansanihi” (أنسانيه) in the verse from Surat Al-Kahf. The pronoun that is in the genitive case (majrur) by means of “ala” (على) is always indeclinable (mabni), whether its pronunciation has a damma or a kasra, as Ibn Malik said: “Every pronoun must be indeclinable, and the pronunciation of what is in the genitive case is like the pronunciation of what is in the accusative case.”