...The Scholars of usool have deduced from the Book and the Sunnah many usool (fundamental principles), upon which they have built many rulings; by which they have also benefited themselves and benefited others.
Amongst these usool (fundamental principles):
 "Al-yaqeen laa yazoolu bish-shakk [certainty is not invalidated by doubt]."
Under this principle they have entered many ?ibaadaat (acts of worship), mu?aamalaat (social interactions) and huqooq (rights). So whosoever entertains a doubt regarding any of that, should return to the asl of certainty. They also deduce: "al-aslut-tahaarah fee kulli shay [The basis concerning all things is that they are pure]." And: "al-aslul-ibaahah illaa ma dallad-daleelu ?alaa najaasatihi aw tahreemihi [The asl (basic principle) is permissibility of using anything, except when there exists an evidence indicative of its impurity or prohibition]." And: "The asl is freedom from accountability concerning obligations towards the creation, until a proof is established to the contrary." And: "The asl is the continuation of accountability concerning the obligations to the Creator, and to His servants, until there is certain proof of freedom and discharging."
 And from them is that: "Al-mashaqah tajlibut-tayseer [difficulty brings about ease]."
Based upon this are all the rukhas (concessions) allowed during a journey, and a lightening of ?Ibaadaat (acts of worship), mu?aamalaat (social transactions), and other matters.
 And from it is their saying: "Laa waajib ma?al-?ajaz wa laa muharram ma?ad-daroorah [there is no obligation with inability, nor is there any prohibition with necessity]."...