if he is unable to have intercourse because of illness and she seeks annulment, then the marriage is annulled—unless the illness is known, or most likely, to be one that will pass through treatment or a change in circumstances. In that case, she has no right to annulment, because its disappearance is to be awaited.
His statement, “once every third of a year”: the evidence is that Allah, Exalted is He, says:
“For those who swear abstinence from their wives, there is a waiting period of four months. Then, if they return, Allah is surely All-Forgiving, Most Merciful. But if they resolve upon divorce, then Allah is All-Hearing, All-Knowing.” [al-Baqarah]
Allah has thus set for him four months. An oath of abstinence neither waives an obligation nor imposes something that is not obligatory. If he had been required to have intercourse in less than four months, that would have been obligatory upon him, and the period of abstinence would have been less than four months. Likewise, if intercourse were not obligatory upon him at least once every four months, he would not be compelled to do so by the oath of abstinence. Thus, an oath of abstinence neither imposes an obligation nor waives one. Since Allah set for him four months, it is understood that what is obligatory is for him to have intercourse with her once every four months.
However, this reasoning is unsound, because an oath of abstinence is a circumstance that arises contingently: the man has sworn not to have intercourse with his wife. So long as the man has taken this oath, we say: in consideration of your situation, your oath, and your sworn pledge, we grant you this period of respite. If you have intercourse and return to your wife, then so be it; but if you do not have intercourse, the marriage is annulled. As for one to whom this circumstance has not arisen, and for whom there is no reason to grant a delay, then what is obligatory is that he live with her honorably. Allah, Exalted is He, says: “Live with them honorably.” [al-Nisaʾ: 19] It is never honorable conduct for a young man to marry a young woman and then have intercourse with her only once every four months.
The correct view, then, is that he must have intercourse with her in accordance with what is customary and proper. A distinction is made between a young woman and an elderly woman: each is to be approached in a manner that satisfies her desire.