His statement, “from the time he irrevocably separates from her”: irrevocable separation occurs with every separation in which return is not possible, or upon completion of the waiting period in a revocable divorce. For example, a man gives his wife her third and final divorce on the last day of Dhu al-Hijjah in the year 1400 AH. She thereby becomes irrevocably separated from him, and gives birth on the twenty-eighth of Dhu al-Hijjah in the year 1404 AH. The child’s lineage is ascribed to him, because she gave birth one day short of four years from the time he irrevocably separated from her.
Another example: a man divorces his wife on the twenty-ninth of Dhu al-Hijjah in the year 1400 AH, and she gives birth on the twenty-ninth of Muharram in the year 1405 AH. The nature of the divorce must then be considered. If it was irrevocable—meaning that it was the third and final divorce—the child is not his, because the period exceeds four years.
If, however, the divorce was revocable, it is known that the waiting period of a woman in a revocable divorce is three menstrual cycles, or three months, according to her circumstances. The child is then ascribed to him, because she does not become irrevocably separated from him merely by the revocable divorce; rather, only when her waiting period has ended. The four-year period is then calculated from that point.
“And he is not judged to have reached puberty if there is doubt concerning it. Whoever acknowledges having had intercourse with his slave woman, whether vaginally or otherwise, and she gives birth after six months or more, her child is ascribed to him—unless he claims that he observed istibrā’ and swears to it, ……”
His statement, “And he is not judged to have reached puberty if there is doubt concerning it”: this applies, for example, to a ten-year-old boy who marries, has intercourse with his wife, and she bears a child, in which case the child is ascribed to him. But is he judged to have reached puberty? He is not judged to have reached puberty if we are uncertain about it—for example, if his pubic hair has not grown, he has not completed fifteen years, and we are uncertain whether he has ejaculated: we do not know whether he has ejaculated or not. Thus, we do not judge him to have reached puberty, because puberty entails numerous legal rulings. We ascribe the child to him despite the uncertainty as a precautionary measure to preserve the lineage and protect it from being lost. The Lawgiver is especially concerned that lineage be established, so it is affirmed on the slightest basis of doubt. But as for imposing obligations upon him or treating him as an adult while doubt remains, then no: certainty is required in establishing puberty.