Why did the vowelization (ʾiʿrāb) of the word "salām" differ in the story of Prophet Abraham with his guests in the Holy Qur’an, appearing once as "salām" and another time as "salāmā," even though it seems to perform the same linguistic function?

The word "salām" (peace) differs in the greeting of Ibrahim's guests from his reply to them. The guests said "salāman" (peace) with the accusative ending (fatha), which is an absolute object (mafʿūl muṭlaq) for an omitted verb, estimated as "Sallimū salāman" (they offered a greeting of peace). As for Ibrahim's reply, "salām" with the nominative ending (ḍamma), it is a subject (mubtadaʾ) whose predicate is omitted, estimated as "Salām ʿalaykum" (peace be upon you). Ibrahim's reply is preferred because the nominal sentence indicates permanence and continuity, and it is more eloquent than the verbal sentence. This aligns with the Almighty's saying: "And when you are greeted with a greeting, greet [in return] with one better than it or [at least] return it [in a like manner]." Among the useful tafsirs are: Tafsir (definition) al-Qurtubi, Tafsir Ibn Kathir, Tafsir al-Tahrir wa al-Tanwir by Ibn Ashour, and Tafsir Adhwa' al-Bayan by al-Shinqiti.