Shah Waliullah Muhadith Dehlawi (Allah have mercy on him) said,
‘A type of nifaaq (hypocrisy) is that an individual affirms verbally and in his heart to the commands of Allah and His prophet (Allah bless him and give him peace) but by committing sinful activities via his tongue, heart (mind) and genitals he is totally surrounded by transgressions.
Hence, an individual who is thoroughly annihilated in sinful activities. That is, committing sins has become an instinct and a part of his personality. This individual is a munafiq (hypocrite).
This type of hypocrisy can exist with eman (belief).
The noble Companions (Allah be pleased with them) were afraid of this type of hypocrisy.’
Taharet e qalb, page 69