Ubaydullah bin Abi Yazid narrates from his father that a man married a woman who had a daughter from another husband, and he had a son from another wife. The boy committed zina with the girl, and a pregnancy became apparent. When Sayyiduna Umar (may Allah be pleased with him) came to Makkah, the matter was brought before him. When the two of them were asked, both confessed, so Sayyiduna Umar (may Allah be pleased with him) had the prescribed punishment (hadd) carried out on both of them. Sayyiduna Umar (may Allah be pleased with him) was keen to join the two of them (in marriage), but the boy refused.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13875