What constitutes obstruction (Adhl) in marriage, and what is the ruling regarding the required dower (Mahr)?

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Obstruction means preventing a woman from marrying a suitable match when she requests it and both parties desire the union. It is irrespective of whether she requests the marriage with the full dower of a peer (mithl) or less. This is the position of Shafi'i, Abu Yusuf, and Muhammad. The evidence is the incident involving Ma'qil ibn Yasar, where the Prophet permitted the marriage even though the guardian initially refused due to a prior divorce. The Prophet also advised a man seeking to marry to "seek even a ring of iron," and approved a woman's marriage for two sandals.