Maulāna Ashraf ῾Ali Thānvi rehmatullāhi ῾alayh replied to a questioner that every Muslim has Nūr ul Imān in him, whether its effects are apparent or not.

A similitude of this is like a handsome person who blackens his beautiful face and thus conceals his beauty. Then as soon as he washes his face with soap, the beauty shines like the full moon. Similarly, the Nūr ul Imān of most of Muslims has been concealed due to increase in disobedience (of AllāhÂ’s commandments), but inshāÂ’allāh as soon as they repent and increase in their Istighfār, their hearts will shine with Nūr.

Malfuzāt Hakīmul Ummat Malfuz # 412 – vol. 1 pg. 311