Question: What is the ruling on Takfeer (declaring a Muslim as a disbeliever)? In Egypt, there is a group that declare Muslims as Kuffaar (disbelievers) for committing sins other than Shirk (associating others with Allaah in His Divinity or worship). Can committing minor or major sins render someone a Kaafir despite their declaration of the Shahaadah (Testimony of Faith)?
Answer: Major sins differ with respect to the gravity of the offence; some of them are Shirk and others are not. Ahl-ul-Sunnah wal-Jamaa`ah (adherents to the Sunnah and the Muslim mainstream) do not declare Muslims to be Kuffaar if they commit sins other than Shirk, such as killing, drinking alcohol, Zinaa (sexual intercourse outside marriage), theft, consuming orphans’ property, slandering chaste Muslim women, and consuming Ribaa (usury), and other major sins. In these cases, the ruler should carry out the penalty prescribed for the sin they commit, such as Qisaas (just retaliation), Hadd (prescribed punishment), or Ta`zeer (discretionary punishment)… read more here.