Explanation of this hadith:
Narrated Abu Huraira:
I have memorized two kinds of knowledge from Allah’s Apostle . I have propagated one of them to you and if I propagated the second, then my pharynx (throat) would be cut (i.e. killed).
[Bukhari :: Book 1 :: Volume 3 :: Hadith121 ]
Hafidh Ibn Hajar al Asqalani (rahimahu Allah) said in his book “Fath al Bari”, in the explanation of this hadith:
(The scholars took this type of knowledge, that he (Abu Hurairah) didn’t transmit\spread, to mean the hadiths that show the names of the Amirs (leaders) of evil, their conditions and era/period.And Abu Hurairah used to point to some of it without declaration, fearing for himself from them, like his saying: I seek refuge to Allah from the head of the sixty, and the leadership of the youth , pointing to the khilafah of Yazid bin Mu’awiyyah, because it was in the year sixty after Hijrah.And Allah answered the duaa of Abu Hurairah, so he died a year before it…Ibn al Munir (683 A.H.) said: the Batiniyyah made this hadith as a means to making their falsehood correct, in which they believed that the shari’ah has a dhahir (apparent\outer knowledge) and batin (hidden\inner\secret knowledge), and the result of that batin is dissolution of the deen.
He said: Abu Hurairah meant by his saying: “would be cut ” meaning: the people of injustice would cut his head off if they heard his criticizing\finding fault with their actions ….. , and what supports this is that the written hadiths, if they were from ahkam (rulings), he wouldn’t be able to conceal it, because of what he mentioned in the first hadith of the ayah that condemns who conceals knowledge.and other said: it could mean things related to signs of the hour, the changing of conditions, and the fierce battles at the end of time, so then the ones who are not familiar with it would reject it…)
And Imam Ibn Battal (449 A.H.) -rahimahu Allah- mentioned in his sharh (explanation) of this hadith in sahih al Bukhari, that the knowledge that Abu Hurairah didn’t spread was related to fitan (trials).Also, a similar explanation is given by Imam adh Dhahabi rahimhu Allah in his books “as Siyar”.So basically, that knowledge that was not revealed is related to things in future, and trials (fitan), it has nothing to do with rulings in shari’ah, that are guidance to mankind which every Muslim should and needs to know, and is not allowed for one to conceal.