Ibn Taymiyah: Explanation of the hadith, Islam is 5…
The Prophet SAWS said: ‘Islam is founded upon 5: testifying that there is no god except Allah and that Muhammad is the Messenger of Allah; establishment of prayer; paying of zakat; fasting Ramadan; and pilgrimage to the House for whoever is able to [make] a way thereto.”
Shaykh Ibn-Taymiyah said:
If there is, among the outward actions that Allah made obligatory, more than these five, then why did he [, the Prophet] say: Islam is these five?
Some people have answered that these  are the more visible and the more powerful symbols of Islam, and by the slave’s accomplishing of them his Islam is completed; and by his leaving them is indicated the dissolution of the bond of his being bound [in Islam].
The more precise explanation is: that the Prophet mentioned the religion that renders up the slave to his Lord absolutely, namely the right of Allah upon individuals, of exclusive worship. So He made it a duty for each one who was capable of it that he worship Allah by it, dedicating the religion purely to Him; and this [religion] – it is [made up of] the five.
[As to] what is similar to that [in being obligatory], then it is what is obligatory according to occasions and exigencies, and so the duties [according to circumstances] thereof do not extend universally to all people.
Rather: [these other obligations comprise] either:
[1.] the collective obligations – such as jihad, and commanding the good and forbidding the evil, and what [necessarily] follows [from] that by way of authority, and governance and the issuing of legal dicta, and [scholarly] inquiry, and transmission of hadith, and other [such duties]; or
[2.] the occasional obligations of the rights of individual persons. By [that right] is specified the one on whom it is obligatory to fulfil it, and it is avoided by annulment, and when the matter is achieved, or by acquittal – whether by his releasing or by the accomplishment of the matter…
…For example: settlement of debts; restitution of the usurped [thing], and of loans, and of deposits for safe-keeping; and just restitution of wrongs respecting blood relations and properties and lands – indeed these are rights of individual persons, and when they release from them, [these rights] are voided, being binding on one person, not on another, in one circumstance, not in another.
They are not incumbent upon every competent slave [of Allah] as is unmixed worship of Allah. That is why the Muslims share in them with the Jews and the Christians.
The five [however, are obligations of a kind quite] different, for indeed these are among the distinguishing [things] of the Muslims [i.e. unique and restricted to the Muslims].