We have already seen in the article ‘Difference between ‘Resalat’ and ‘Nabuwwat’ that there is difference between a ‘Rasool ’ and a ‘Nabi’. Among others, one difference between ‘Resalat’ and ‘Nabuwwat’ is pertaining to type/nature of ‘wahi’. The various types of ‘wahi’ described in my article ‘Wahi, Intuition and their Implications’ are summarized as below:-
i. A ‘Rasool’ receives complete Book through Gabriel (as) in the form of Allah’s words whereas a ‘Nabi’ receives partial Book through Gabriel in the form of Allah’s ideas/ ‘wahi’ translated by Gabriel (e.g. Hadith e Qudsi) or ‘Nabi’ himself (e.g. Hadith e Rasool). A Book received by a ‘Nabi’ is not in the form of Allah’s words. A 'Rasool' may also receive 'wahi' directly from Allah, without mediation of Gabriel; such 'wahi' is translated by the 'Rasool' himself.
ii. We have also seen in the article ‘Types of Prophet-hood and Criteria of Punishment’ that some Prophets are ‘rasool’ and ‘Nabi’ combined. Such Prophet being ‘rasool’ receives complete Book through Gabriel (as) in the form of Allah’s words and being Nabi receives, in respect of the Book he receives, Allah’s ideas/ ‘wahi’ which is translated by Gabriel (e.g. Hadith e Qudsi) or the Nabi (as) himself (e.g. Hadith e Rasool). Such a 'wahi' received as a Nabi by a 'Rasool' and 'Nabi' combined and translated by Rasool himself has been called as 'words of Rasool' (al-haqah-40); and such a 'wahi' translated by 'Gabriel' has been called as words of Gabriel (al-takwir-19). Such ‘wahi’ received as a Nabi by a ‘Rasool’ and ‘Nabi’ combined OR received by 'Rasool' directly from Allah without mediation of Gabriel is called Sunnah of that ‘Rasool’ and ‘Nabi’. In other words, Sunnah of a ‘Rasool’ is Allah’s ideas/ ‘wahi’ regarding the Book revealed to him; Sunnah is the interpretation of Allah’s words/ Book revealed to a Rasool; such interpretation is done either by the 'Rasool' himself or by Gabriel and is based on 'wahi' sent by Allah.
We may conclude that ‘Sunnah’ is the second name of Allah’s Book. A person disbelieving in Sunnah, in fact, disbelieves in Quran.