A husband denies that the child is his: what is the procedure in Islam?

The only Shariah-recognised way for a husband to deny paternity of a child born within marriage is liʿan: the husband swears four times before a judge that he is truthful, and the fifth time invokes Allah's curse upon himself if he is lying; the wife may avert it with a similar counter-oath. The effect is that the marriage is ended permanently and the child is attributed to the mother only. Liʿan must be done promptly upon learning of the pregnancy or birth, not years later. Accusing one's wife of zina without proof is a major sin. In Malaysia, liʿan can only be carried out through the Syariah Court. Consider counselling and legal advice before taking this step. See liʿan.