Some jurists considered religious devotion the sole criterion of suitability, citing the Prophet’s words, peace and blessings be upon him: “So marry the woman of religion—may your hands be rubbed with dust.”
Others maintained that in the ḥadīth pedigree and wealth are to be understood as subdivisions of religion, and that nothing is excluded from suitability save what unanimous agreement has excluded—namely, that physical beauty is not one of its conditions. Everyone who permits annulment of marriage on account of bodily defects treats sound health as an element of suitability; on that basis beauty, too, carries a certain weight.
Within the Mālikī school there is also no dispute that poverty warrants the annulment of a father’s marriage of his virgin daughter—that is, when the prospective husband is poor and unable to provide for her. Hence they reckon material ability part of suitability, a view Abū Ḥanīfah does not share.
As for freedom, the school likewise agrees that it is an aspect of suitability, for the established Sunnah gives a slave-woman the option of leaving her husband when she is emancipated. Concerning the dower equal to that of her peers (mahr al-mithl), Mālik and al-Shāfiʿī hold that it is not among the conditions of suitability and that a father may marry off his virgin daughter for less than that amount. A previously married, responsible woman who accepts such a dowry leaves her guardians no grounds to object. Abū Ḥanīfah, by contrast, counts the peer dowry as part of suitability.
Their disagreement stems, with regard to the father, from the question of whether he may reduce his virgin daughter’s dower. With regard to the thayyib, they differ over whether guardianship over the amount of dower lapses for a competent woman as it does in her other financial transactions, or whether it remains in place because guardianship over the marriage contract itself remains, and the dowry arises from that contract. One would have expected the first view to belong to those who require guardianship, yet the opposite proved true.
A famous issue tied to the laws of guardianship is whether a guardian may marry his ward to himself. Al-Shāfiʿī forbade it by analogy to the judge and the witness, neither of whom may rule or testify in his own favor. Mālik allowed it, basing himself—so far as I know—only on the reports that the Messenger of Allah, peace and blessings be upon him, married Umm Salamah without a guardian because her son was still a minor, and that he emancipated Ṣafiyyah and made her emancipation her dowry. Al-Shāfiʿī’s general principle is that the Prophet’s marriages are specific to him unless evidence shows they are general, because of the many special rulings that applied uniquely to him; nonetheless, his judgment wavered when it came to the supreme ruler (imām al-aʿẓam).