Tafsir of As-Saffat 37:56

(He said) meaning the speaker to his companion, (By Allah, you had almost ruined me.)

(Meaning: You had almost caused me to perish. In the recitation of ‘Abdullah [ibn Mas‘ud], it is [“la-tughwin” - you had almost led me astray]. The [“in”] is the lightened form of the heavy [“inna”], and the [“lam”] is the differentiator [al-fariqah]. In al-Bahr, it is stated that the oath here expresses astonishment at his own safety from him, as his companion had nearly brought about his ruin.)