Tahdhib al-Asma’ wa al-Lughat, Imam Nawawi, Publish: Dar al-Kutub al-Ilmiyah, Beirut/Lebanon

Shaykh al-Islam, Imam al-Nawawi said: al-Bid`ah in the Law is the innovating of what did not exist in the time of the Messenger of Allah and is divided into “excellent” and “bad” (wahya munqasimatun ila h.asana wa qabih.a). The Shaykh, the Imam on whose foremost leadership, greatness, standing, and brilliance in all kinds of Islamic sciences there is consensus, Abu Muh.ammad `Abd al-`Aziz ibn `Abd al-Salam – Allah have mercy on him and be well-pleased with him! – said toward the end of his book, al-Qawa`id [al-Kubra]: “Innovation is divided into ‘obligatory’ (wajiba), ‘forbidden’s (muh.arrama), ‘recommended’s (manduba), ‘offensive’s (makruha), and ‘indifferent’s (mubaha). The way [to discriminate] in this is that the innovation be examined in the light of the regulations of the Law (qawa`id al-shari`a).If it falls under the regulations of obligatoriness (ijab) then it is obligatory; under the regulations of prohibitiveness (tah.rim) then it is prohibited; recommendability, then recommended; offensiveness, then offensive; indifference, then indifferent.”

Imam Nawawi said Imam Bayhaqi Narrated with sound chain Imam Shafi’I said: Innovation is two types (al-bid`atu bid`atân): approved innovation (bid`a mah.mûda) and disapproved innovation (bid`a madhmûma). Whatever conforms to the Sunna is approved (mah.mûd) and whatever opposes it is abominable (madhmûm).’ He used as his proof the statement of `Umar ibn al-Khat.t.âb (ra) about the [congregational] supererogatory night prayers in the month of Ramad.ân: “What a fine innovation this is!” [Tahdhib al-Asma’ wa al-Lughat, Imam Nawawi, Volume 003, Page 23]