Verse 15 and 16 of Surah Al-Qasas, with the phrases "Hādha min 'amal al-shayṭān (This is of Satan's doing) and innī ẓalamtu nafsī (Indeed, I have wronged myself)," have long been considered one of the most challenging verses in the discussion of the 'Ismah (Infallibility) of the Prophets (PBUH), as their literal meaning seems incompatible with the position of infallibility. This research focuses on this verse, examining the exegetical and theological foundations of the exegetes and analyzing their strategies in confronting this apparent contradiction. The main question is: Based on what theological principles did the exegetes interpret the verse, and what methods did they adopt to safeguard the principle of 'Ismah? The research methodology is based on a combination of exegetical-hermeneutical analysis and a comparative study of exegetical discourses. The findings indicate that three main strategies stand out among the prominent exegetes: First, shifting the pronoun's reference and attributing "hādha" to the quarrel or the Egyptian's action; Second, redescribing the nature of the act by emphasizing the unintentionality of the killing; and Third, re-theologizing the concept of sin by reducing it to Tark al-Awla (omission of the better/preferable) and hermeneutically reinterpreting the seeking of forgiveness (istighfar). The novelty of this research lies in analyzing the relationship between the theological principles and the exegetical strategies, instead of merely collecting opinions, demonstrating that these principles function as a hidden grammar behind the interpretation. Finally, the present study emphasizes the necessity of simultaneous attention to the linguistic, social, and theological dimensions in exegetical analyses and offers a methodological model for engaging with the Mutashābih (ambiguous/allegorical) verses of the Qur'an.