"...If the party liable is mentally deficient, or weak, or unable Himself to dictate, Let his guardian dictate faithfully, and get two witnesses, out of your own men, and if there are not two men, then a man and two women, such as ye choose, for witnesses, so that if one of them errs, the other can remind her. The witnesses should not refuse when they are called on (For evidence)." - Quran 2:282 (read more)

"O Allah's Apostle! We asked you for mounts, but you took an oath that you would not give us any mounts; we think that you have forgotten your oath.' He said, 'It is Allah Who has given you mounts. By Allah, and Allah willing, if I take an oath and later find something else better than that. then I do what is better and expiate my oath.'" - Sahih Bukhari 7:67:427 (read more)

"Islam says that these three groups [Jews, Christians, and Magians] may be given the choice: they may enter Islam or they may pay the jizyah and feel themselves subdued. Some of the scholars are of the view that others may also be given the choice between Islam and jizyah, but the most correct view is that no others should be given this choice, rather these three groups are the only ones who may be given the choice, because the Prophet (peace and blessings of Allaah be upon him) fought the kuffaar in the Arabian Peninsula and he only accepted their becoming Muslim." - Islam Q&A