A man who had had intercourse with his wife's slave-girl was brought to Sayyiduna Umar (may Allah be pleased with him), and he (may Allah be pleased with him) did not stone him but flogged him a hundred lashes.
This is munqati' (disconnected); and if it is authentic, it seems he claimed ignorance, so he gave him a discretionary punishment and did not stone him, and Allah knows best.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 17083