Explanation
In Fiqh Hanafi, Fard refers to an obligation established by definitive (qat'i) evidence — such as the Quran or mutawatir Hadith — and its denial amounts to disbelief. Wajib, on the other hand, is an obligation based on probable (zanni) evidence, and while its deliberate omission is sinful, denying it does not take one out of the fold of Islam. The other three Sunni schools — Shafi'i, Maliki, and Hanbali — treat Fard and Wajib as synonymous, making no such distinction.
Good to know
The Hanafi school, founded by Imam Abu Hanifa (d. 767 CE), is the oldest of the four major Sunni schools of jurisprudence. This nuanced classification of legal rulings into categories like Fard, Wajib, Sunnah, Mustahab, Mubah, Makruh, and Haram reflects the Hanafi school's meticulous approach to usul al-fiqh (principles of jurisprudence). The Fard/Wajib distinction has practical implications, particularly in matters of worship such as Salah, where missing a Fard act invalidates the prayer while missing a Wajib act requires prostration of forgetfulness (Sajdah Sahw).