It was said that Sheikh Kolayni was the main Shia scholar of 3rd Century AH. He was born concurrent with the Imamate of 11th Infallible Imam of Prophet of Islam’s Household, Imam Hassan Askari (Peace be upon him), and was contemporary to the four especial deputies of the 12th Infallible Successor to Prophet of Islam, Imam Mahdi (May God hasten his reappearance). Meanwhile, due to the social restrictions imposed on those leading figures, the cultural and scientific responsibility of Shiasm was shouldered by Sheikh Kolayni. This prominent Shia scholar was born into a virtuous and knowledgeable family. Upon the acquisition of preliminary sciences under his father and maternal uncle, he traveled to the cities of Rayy, Qom, Kufa, and Baghdad to benefit from the teachings of Holy Quran and Prophet Mohammad’s Infallible Household, in the best possible manner. In his lifetime, Sheikh Kolayni was witness to the efforts of different sects for deviation of religion. Upon the appropriate understanding which he maintained about his era, his top priority was to safeguard the remarks made by the Prophet of Islam’s Infallible Household.

Throughout his blessed life, Sheikh Kolayni compiled valuable books. However, his most important book is Kaafi, which took him twenty years to compile. Kaafi is the first book of the four accredited Shia books of hadith. This book has been a source of reference for Shia hadith scholars and theologians for the past eleven centuries.

Sheikh Kolayni has presented 16,000 hadiths cited from the Prophet of Islam, Mohammad, and His Infallible Household. This book maintains three sections; the first section of which is comprised of eight chapters. The first section is comprised of ideological and ethical discussions. In this section, Sheikh Kolayni has initially referred to several hadiths, while pointing out the importance of wisdom and prudence in understanding Islamic teachings. Thereafter, he has studied the virtue of acquisition of knowledge in order to clarify the importance of knowledge and vigilance in proof of ideological principles. Then, he has pointed out the most important ideological principle, which is monotheism. Another chapter of this section revolves round ethical topics such as modesty, patience, frugality, virtues of prayers, virtues of Holy Quran, manners, and so forth. The contents of this chapter of the first section of this book are highly appealing, diverse, and understandable for everyone. 

The second section of this book covers theological hadiths on topics such as prayers, zakat, Hajj Pilgrimage, and fasting. This section is often used by theologians. The third section of the book “Kaafi’ covers 597 hadiths, on different topics such as the sermons and letters of the Infallible Imams, and historical tales.

Sheikh Kolayni, who compiled this book, was born during the Imamate of 11thInfallible Imam of the Prophet of Islam’s Household, Imam Hassan Askari (Peace be upon him), and was contemporary to the four especial deputies of Imam Mahdi. Therefore, he cited some of the hadiths with only three mediators, which is one of the strong points of this book. In Kaafi, hadiths have been grouped under short and clear headings, which show the contents of each section.

In the Introduction of this book, Sheikh Kolayni has said that a hadith is valid and correct which is in line with the Book of God.
The prominent Shia scholar, Sheikh Mofid, notes: “Kaafi is one of the main Shia books; which Shia scholars have benefitted from, more than any other book.”

Sheikh Kolayni passed away at the age of 70 in the year 328 AH, in Baghdad, concurrent with the start of the Major Occultation of Imam Mahdi (May God hasten his reappearance). His tomb is in Baghdad, on the eastern banks of River Tigris, next to Baghdad’s old bridge.