Who is "those who keep themselves pure" referring to in this āyah?

Imām Ibn al-Jawzī (d. 597/1201) summarized the scholars' opinions in his book "Zād al-Masīr" as follows:

1. It refers to those who purify themselves from sins. [Mujāhid, Saʿīd ibn Jubayr, Abū al-ʿĀliyah]
2. It refers to those who purify themselves with water. [ʿAṭāʾ]
3. It refers to those who avoid approaching their wives from behind. [Reported from Mujāhid]