The Quran

قالوا يا لوطُ إِنّا رُسُلُ رَبِّكَ لَن يَصِلوا إِلَيكَ ۖ فَأَسرِ بِأَهلِكَ بِقِطعٍ مِنَ اللَّيلِ وَلا يَلتَفِت مِنكُم أَحَدٌ إِلَّا امرَأَتَكَ ۖ إِنَّهُ مُصيبُها ما أَصابَهُم ۚ إِنَّ مَوعِدَهُمُ الصُّبحُ ۚ أَلَيسَ الصُّبحُ بِقَريبٍ

Muhammad Asad

[Whereupon the angels] said: "O Lot! Behold, we are messengers from thy Sustainer! Never shall [thy enemies] attain to thee! Depart, then, with thy household while it is yet night, and let none of you look back;¹ [and take with thee all thy family] with the exception of thy wife: for, behold, that which is to befall these [people of Sodom] shall befall her [as well].² Verily, their appointed time is the morning [and] is not the morning nigh?"

I.e., in an abstract sense, "to what you are leaving behind" (Razi)- evidently meaning the severing of all associations with the sinful city, and not a physical looking-back.
Cf. 7:83 and the corresponding note, as well as 66:10, where it is mentioned that Lot's wife, who was apparently a native of Sodom, had acted faithlessly towards her husband, i.e., had refused to believe in his prophetic mission; and her story was thereupon "propounded as a parable of those who are bent on denying the truth".