His statement: “If they separate in an invalid marriage before consummation and seclusion, then no dowry is due.” You should know that an invalid marriage is not the same as a void marriage. This distinction is particular to marriage in the Hanbali school, for they distinguish between invalid and void only in two cases. The first is here, in the chapter on marriage; the second is in the chapter on Hajj. In the chapter on Hajj, they say that an invalid Hajj is one in which the pilgrim has intercourse before the first stage of release from consecration: he must continue with it. A void Hajj, however, is one in which he apostatizes—for example, a pilgrim who mocks the verses of Allah and thereby becomes an apostate; his Hajj is then rendered void.
An invalid marriage is one whose invalidity is disputed by the scholars, whereas a void marriage is one whose invalidity is unanimously agreed upon, such as marrying one’s sister. For example, a man may marry a woman and then discover that she is his foster sister; the marriage is void because the scholars are unanimous that it is invalid. An example of an invalid marriage is one contracted without a guardian, without witnesses, or involving a woman who nursed from his mother once, twice, three times, or four times.
His statement, “If they separate in an invalid marriage,” means: in an invalid marriage, “before consummation and seclusion”—that is, before the dowry becomes binding in full—“then no dowry is due.”
An example is a man who marries a woman without a guardian, and is then told that this marriage is invalid. If he divorces her before consummation and seclusion, she is entitled to nothing, because an invalid contract is treated as though it did not exist and has no legal effect.
Must he nevertheless divorce her? Yes, he must, out of consideration for the scholarly disagreement. Some scholars hold that a marriage without a guardian is valid. Thus, another man who wishes to marry her, and who holds such a marriage to be valid, may say, “She remains married to the first husband.” For this reason, the husband is compelled to divorce her; if he refuses, the judge divorces her on his behalf or annuls the marriage.