and their monks as lords besides Allah, as well as the Messiah, son of Mary. Yet they were commanded only to worship one God; there is no deity except Him. Glory be to Him, far above whatever they associate with Him.”
Surah al-Tawbah 9:31

For this reason, this practice has become widespread among groups of ascetics and worshippers within this community who follow religious innovations, departing in this respect from the revealed law and the message of Muhammad—may Allah bless him and grant him peace—even though in other respects they remain within them.

Such is the nature of all innovated spiritual paths: truth and falsehood are mingled within them. It is well known that what these people do constitutes immoral deeds, whether outward or inward.

The Most High has said:

“He said, ‘My Lord has forbidden only immoral deeds—whether committed openly or in secret—sin, unjust aggression, associating with Allah that for which He has sent down no authority, and saying about Allah what you do not know.’”
Surah al-A‘rāf 7:33

The Most High has also said:

“Abandon both outward and inward sin.”
Surah al-An‘ām 6:120

It is reported in the two Sahīh collections, on the authority of Ibn ‘Abbās, Abū Hurayrah, that the Prophet—may Allah bless him and grant him peace—said:

“The eyes commit zina, and their zina is looking. The ears commit zina, and their zina is listening. The tongue commits zina, and its zina is speaking. The heart longs for it and desires it, and the private parts either consummate it or do not.”