Al-Waajib and Al-Fard hold one meaning as they are synonyms (Lafzhaan Mutaraadifaan).

As for what some of the Mujtahideen have said including the Ahnaaf in respect to the Fard being that which has been established by a Daleel Qat’iy (definite evidence) and the Waajib being established by a Daleel Zhanniy (indefinite evidence), then there is nothing within the language or the Shar’a that indicates and guides to making such a differentiation between them.

The reality of this matter is that it is that which the Shaari’ has requested by a decisive request and there is no difference in respect to whether the Talab (request) was established by a Daleel Qat’iy or a Daleel Zhanniy.

The definition of the Waajib or the Fard according to the majority is: It is what the Shaari’ has requested to be done by way of a decisive request (Talab Jaazim) and it is also that which the doer is rewarded and praised/commended whilst its leaver is punished and found blameworthy. Examples of the Fard include: Al-Jihaad, the Sawm of Ramadhaan and ruling by what Allah (swt) has revealed. From amongst the evidences indicating the Wujoob (obligation) of Al-Jihaad is the Qawl of Allah Ta’Aalaa:

This is an Amr Jaazim (decisive command) due to the Qareenah (connotation) in His Qawl (swt):

From among the Adillah (evidences) for the Wujoob (obligation) of fasting in Ramadhaan is the Qawl of Allah Ta’Aalaa:

And the meaning of Kataba (written/prescribed) is Farada (made obligatory). The Qareenah (connotation) for that is the Qawl of Allah ‘Azza Wa Jalla:

The Talab (request) is therefore Jaazim (decisive) because it has requested the sick person or traveller if they were unable to fast, to fast, after the passing of the excuse, a number of days in exchange for those in which they had broken their fast. From the evidences (Adillah) for the Wujoob of ruling by what Allah has revealed is His Qawl Ta’Aalaa:

And also the Aayaat that follow: