According to Ibn Juzayy al-Kalbi (the person given the most credit for summarizing the various views in the Maliki school and also outside of the Maliki school), these acts are:

1) Negating that Allah has Lordship over His creation.

2) Negating that Allah is one in His Entity, attributes, and actions.

3) Worshiping another entity along with Allah (Shirk).

4) Changing one's religion to other than Islam after having learned about Islam and understanding it. (Allah has said that "Whoever seeks other than Islam as a din, it will not be accepted from him").

5) Claiming that Allah can become manifest in His creation (e.g. take the form of a man, concept of Hulool).

6) Believing in reincarnation.

7) Negating any one of His known attributes. Included in this is claiming that the Universe was created by other than Him or that He was born from something else. Included in this also is claiming that the Universe had no beginning in time.

8) Claiming that one has sat alongside with Allah literally speaking or claiming that one has ascended to visit Him literally speaking.

9) Claiming that a person after the time of Prophet Muhammad ibn`Abdullah is a real prophet from Allah (and that Prophet Muhammad is not the last prophet). Included in this is claiming that one has received revelation from Allah (like a prophet).

10) Stating that it is possible that the prophets lied to us.

11) Claiming that the message of Islam is only for Arabs (or only for another chosen group).

12) Claiming that one will enter Paradise (literally) while still in this world.

13) Claiming that the punishment and reward in the next life is only confined to being metaphorical.

14) Calling all of the Companions of the Prophet (all together) disbelievers.

15) Denying any of the necessarily known and obvious parts of the religion (e.g. claiming that formal prayer, fasting in Ramadan, Zakat, and Hajj is not obligatory.

16) Claiming that there is no need to worship Allah externally any more after becoming spiritually advanced. For example, claiming that the formal prayer is no longer wajib after one has reached some high spiritual station with Allah.

17) Denying any part of the Qur'an left by the Prophet (May Allah bless him and give him peace).

18) Intentionally adding to (inserting one's own words into) or changing any part of the Qur'an left by the Prophet (May Allah bless him and give him peace) [Included in this is fabricating obligatory tenets of belief or obligatory acts of worship which have no basis in the primary texts].

19) Claiming that others besides Allah could produce the Qur'an.

20) Claiming that the later scholars/saints (e.g. Imam Malik, Imam al-Shafi`i) were better than the prophets.

{al-Qawanin al-Fiqhiyyah by Ibn Juzayy al-Kalbi: page 323, lines 7-18}