From the Fatawa of Allamah Ibn Baz (rahimahullah)
What is ruling on whoever curses Allah or His Messenger or degrades them? What is the ruling on whoever denies something that Allah has made Wajib or considers something Halal (lawful) that Allah has declared as Haraam (prohibited)? Please provide us with a detailed answer as these evils have widely spread amongst many people.
Whoever curses Allah (Glorified be He), the Messenger Muhammad (peace be upon him), any other messenger, or Islam by any means or degrades or mocks Allah or His Messenger (peace be upon him) is a Kafir (disbeliever) and a Murtad (apostate) in case they ascribe themselves to Islam.
Muslims have unanimously agreed on the foregoing as Allah (Glorified and Exalted be He) says:Surah At-Tawbah, 9:65 Say: “Was it at All�h (عز وجل), and His Ay�t (proofs, evidence, verses, lessons, signs, revelations) and His Messenger (صلى الله عليه وسلم) that you were mocking?” Surah At-Tawbah, 9: 66 Make no excuse; you disbelieved after you had believed.
The prominent scholar Imam Abu Al-`Abbas ibn Taymiyyah (may Allah be merciful with him) mentioned detailed proofs for this issue in his book “Al-Sarim Al-Maslul `ala Shatim Al-Rasul”. Whoever likes to check these proofs can refer to this book, which is very valuable and whose author (may Allah be merciful with him) is distinguished for his vast knowledge of Shar`y (Islamic legal) proofs.
The same ruling mentioned above also applies to whoever denies something Ma`lum minad-din bid-darurah that Allah (Exalted be He) has declared as Wajib or considers it Halal although Allah (Exalted be He) has declared the same as Haraam.
Our Salaf, thus, agreed that whoever denies the obligation of performing Salah (Prayer), paying Zakah (obligatory charity), observing Sawm (Fast) in Ramadan, performing Hajj while able, being dutiful to parents, and so on, is an apostate Kafir in case that they ascribe themselves to Islam. Likely, whoever regards drinking Khamr (intoxicants), undutifulness to parents, usurping people’s wealth and killing them with no valid reason, consuming Riba (usury), and so on, as Halal is an apostate Kafir. Scholars (may Allah be merciful with them) discussed this issue and other issues classified under the nullifiers of Islam in detail in the chapters discussing the ruling on apostates.
Whoever wants to know more regarding this issue may refer to these chapters in the books of various scholars from the Hanbaly, Shafi`y, Maliky, Hanafy and other Schools of Jurisprudence to get the details that are sufficient In sha‘a-Allah (if Allah wills).
No one is to be excused on the plea of being ignorant, as the matters mentioned above are well known for Muslims and the rulings on them are clear both in the Qur’an and the Sunnah.
May Allah grant us success! May peace and blessings be upon our Prophet Muhammad and his family!