Hakim al-Umma Hadhrat Mawlana Ashraf ‘Ali Thanawi (may Allah ahve mercy on him) said,
“The Islamic jurist (fuqaha) and sufi masters have paid due attention to the principle, that if a permissible or desired (mustaheb) action becomes the source of a sin then that action itself will become impermissible.
For example, some intoxicants (like opium) in minute quantities that are non-intoxicating are not impermissible (haram). However, as small quantity can (inadvertently) increase and become intoxicating, they are prohibitted in meager amounts also.
Similarly, permissible speech, sleep and intermingling with others are not sinful in themselves. But (excessive & unrestricted involvement in) these activites eventually lead to indulgence in sin. It is for this reason Sufi Masters prohibit these also (i.e. the well known spiritual struggles (mujahidat) of the path).”
Fiqh e Hanafi kay usul wa zawabet, page 113