Tafsir of As-Saffat 37:153

(Asṭafā) is written with an open hamza, which is an interrogative particle after which the hamzat al-wasl has been omitted. The interrogation here is for the purpose of denial (inkār). The intent is to establish their fabrication and confirm their falsehood. Al-iṣṭifāʾ (choosing) is the taking of the choicest part of a thing for oneself.

Nāfiʿ, in the narration of Ismāʿīl, Ibn Jammāz, a group [of reciters], and Ismāʿīl from Abū Jaʿfar and Shaybah, read it as (Iṣṭafā) with a kasra on the hamza. This is a hamzat al-wasl, which takes a kasra when beginning with it. This reading is explained by the omission of the interrogative particle, due to the indication provided by am (or) that follows, even if it is not explicitly functioning as a correspondent particle, given its frequent usage with it.

It is also permissible to maintain the statement as an informative report (ikhbār), either by assuming an elided verb of speech—meaning they say: "He has chosen..."—or by treating it as a substitution for their saying "Allah has begotten," provided it is not an intrusive element between two related clauses. The most appropriate interpretation is that of omitting the particle, which brings the discussion to a close. So contemplate this.