Indeed all praise is due to Allāh. We praise Him, seek His aid and ask for His forgiveness. We seek refuge with Allāh from the evil of our own souls and from the evil of our wicked actions. Whomsoever Allāh guides, then none can misguide; and whomsoever Allāh misguides, then none can guide.
I testify that none has the right to be worshipped except Allāh, alone without any partner; and I testify that Muḥammad is His slave and Messenger. May abundant peace and blessings be upon him, his family and all of his Companions.
A number of illustrious scholars have written concerning the major sins. Imām al-Dhahabī (d. 748H) and Shaykh al-Islām Muḥammad b. ʿAbd al-Wahhāb (d. 1206H) compiled books on this subject. Abū Najā Mūsá b. Aḥmad al-Ḥajjāwī al-Ḥanbalī (d. 968H) wrote a classical poem about the major sins titled Manẓūmah al-Kabā’īr.
Others discussed this subject in larger works like Imām Ibn al-Qayyim (d. 751H) in his book ʿIlām al-Muwaqqiʿīn.
All of this shows the importance of this topic, and that it is a subject that every Muslim needs to learn about.
If Imām al-Dhahabī said that many people in his time were unaware of many of the major sins – and this was nearly seven hundred years ago – then what about our time and what about the Muslims who were born and raised in non-Muslim lands?
For this reason, I wanted to compile a primer for Muslims who aspire to learn about the major sins. I decided to follow a familiar tradition of our scholars and compile forty Ḥadīth concerning the major sins, walking upon their path.  Muslims all over the world are well acquainted with the forty Ḥadīth of al-Nawawī concerning the fundamental principles of Islam. However, I do not know of anyone who has compiled forty Ḥadīth about the major sins.
I also included introductory chapters to help the reader fully grasp this topic with an accurate and beneficial understanding.
The questions at the end of each Ḥadīth are based on my lessons explaining this book. The aim is to author a teacher’s version at a later date – if Allāh Wills.
Hopefully, this approach will be beneficial to all Muslims and assist them to recognize these sins and the dangers associated with them, so that they can be avoided.
I ask Allāh to accept this small effort and make it sincerely for His Sake, and pardon me for any shortcomings.
25th of April 2019 [19th of Shaʿbān 1440]
 As for the Ḥadīth: “Whoever preserves forty Ḥadīth for my nation relating to their religion, then Allāh will resurrect him among the jurists and the scholars,’ then it is Ḍaʿīf [weak]. Shaykh Albānī discusses the weakness of these narrations in al-Ḍaʿīfah (no. 4589).