All praise be to Allaah, Lord of the Worlds.
As for which books one may depend on for the different branches of knowledge, then this is a vast topic, and again, the answer to this varies according to people’s backgrounds in different lands. This is because in each land, one field of learning or way or mode of thinking may be easier than another, but the source of all good and blessings is that one seeks help from Allaah in acquiring knowledge inherited from the Prophet, sallallaahu `alayhi wa sallam, because that is what is truly fit to be named knowledge. Anything else is either not knowledge at all even though people call it so, or it is knowledge which is not beneficial, or it is beneficial knowledge, in which case it is necessarily true that there exists in the inheritance of Muhammad, sallallaahu `alayhi wa sallam, that which replaces it, being similar to it or better than it.
Thus the person’s effort should be to understand the purposes of the Messenger, sallallaahu `alayhi wa sallam, in his commands, prohibitions and his various other sayings. When the heart is contended that something is indeed as the Messenger, sallallaahu `alayhi wa sallam, intended, then he should not waver from it as far as possible, whether it is regarding his duties to Allaah or to the people. In all branches of knowledge, he should strive to hold firmly to principles narrated from the Prophet, sallallaahu `alayhi wa sallam; if he is in doubt regarding any matter about which the people of knowledge have differed, then he should supplicate to Allaah with the du`aa which appears in Saheeh Muslim narrated by `Aa’ishah, radiyallaahu `anhaa, that when the Messenger, sallallaahu `alayhi wa sallam, stood for the night prayer, he would say,
“O Allaah! Lord of Jibreel, Meekaa’eel and Israafeel, Originator of the Heavens and the Earth, Knower of the Unseen and the Present! You judge among your slaves regarding what they have differed in. Guide me to the truth regarding that in which they have differed, for truly, You do guide whomsoever You wish to a path that is straight.”
This is because Allaah the Exalted has said, as narrated by His Messenger from Him,
“O My slaves, all of you are astray except those that I have guided, so seek guidance of Me and I shall guide you.” [Muslim]
As for a description of good books and compilations: people will have heard from me what Allaah has made easy on other occasions. I will say this much now, that out of all the compiled books which have been divided into chapters, there is none more beneficial than the Saheeh of Muhammad bin Ismaa`eel al-Bukhaaree. However, this alone is not enough to cover all the major principles of knowledge, nor can it fulfill all the objectives of one who seeks to dive deep into the various branches of knowledge. It is imperative that other ahaadeeth, as well as the words of the people of understanding and the people of knowledge of different specialised fields be known, for the Ummah has progressed tremendously in all fields of learning. He whose heart Allaah enlightens He guides him through what reaches him; but he whose heart Allaah blinds, many books only increase him in confusion and misguidance, as the Prophet, sallallaahu `alayhi wa sallam, said to Ibn Labeed al-Ansaari,
“Did the Jews and Christians not have the Tauraat and the Injeel? So what benefit did these bring them?” [al-Bukhaaree in Khalq Af`aal al-`Ibaad, an-Nasaa’ee, Ahmad, al-Haakim, ibn Hibbaan, Saheeh]
So we ask Allaah Almighty that He sustains us with guidance and firmness, instills in our hearts our correct direction, protects us from the mischief of our own selves, that He does not allow our hearts to deviate after giving us guidance and that He bestows on us Mercy from Him, for He is the Most Generous.
All Praise be to Allaah, Lord of the Worlds, and His Blessings be on the most noble of the messengers.