Imam Ahmad Zarruq رحمه الله said in under the 4th Principle of his Qawa’id al-Tasawwuf:
“There is no tasawwuf without fiqh; because there is no other way to understand the commandments of Allah that concern the exterior except by fiqh. and fiqh is nothing without tasawwuf; because deeds have no meaning unless accompanied by sincerety (sidq) and dedication (tawajjuh).
Neither of them is of any use without true belief [wa la huma illa bi iman]. that is, neither of them [fiqh/tasawwuf] is valid unless true belief is present in the first place.”