,,Our eminent grandmaster, Khalil Ibn Ghazi Al-Qazwini, meritorious scholar, theologian, principled, grasper of the subtleties of reasoning, endowed with formidable intellectual capacity, one of the most respectable among the famous scholars and most perfect among the meritorious giants of our time [ … ] and among his most peculiar statements is that the master (Al-Mahdi) saw Al-Kafi in full and approved of it.” [Riyad-ul-Ulama’, Volume 2, page 261]
,,It has become famous among the knowledgeable that the Book (Al-Kafi) was shown to the Riser (Al-Mahdi), whereupon he approved of it and said: ﴾Sufficient for our followers.﴿” [Ahamiyyat-ul-Hadith, page 8]
,,Thus, the books of this scholar, Muhammad ibn Ya’qub (Al-Kulaini) and his narrations are available at the time of the mentioned representatives (ambassadors) in a time for which one can find a way to verify his traditions and authenticate his books.” [Kashf-ul-Mahajjah, page 220]
,,Some of our scholars believe that it (Al-Kafi) was shown to the Riser (Al-Mahdi), whereupon he approved of it and said: ﴾Sufficient for our followers.﴿” [Riyad-us-Salikin, Volume 1, page 77, footnote]
,,A group of preeminent authors favored that he (Al-Kulaini) was in contact with the deputies of Imam Muhammad Ibn Hasan (Al-Mahdi), who in turn were in contact with him, as stated by the Traditionarian An-Naisaburi in his book Munyat-ul-Murad, as well as Sayyid Ali Ibn Tawus and others besides the two of them and these proceeded from this stage to that the messengers showed Al-Kafi to the Imam and he agreed to follow it and they adhered to what was reported from him which was that he said: ﴾Al-Kafi is sufficient for our followers.﴿” [Dirasat Fi l-Hadith, page 127]
,,Yes, it can be said that some parts of Al-Kafi were shown to the Imam (Al-Mahdi), whereupon he approved and agreed with it just as there is no shortage, that some representatives and eminent experts have seen the other parts of Al-Kafi and thus our statement represents a middle ground between the statements in which exaggeration or understatement was evident.﴿” [Al-Kulaini Wa l-Kafi, page 397]
One of the names of God is the Sufficient (Al-Kafi) [Read here]. In a supplication, the Prophet (s.) and Ali (a.) are referred to as the Sufficient Ones [Read here]. Thus, the word “sufficient” (Kafi) does not at all mean that everything else is useless.