Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: I heard Sayyiduna Umar (may Allah be pleased with him) saying: "Stoning is in the Book of Allah for every married man and woman who commits adultery, when they either confess, or there is evidence, or pregnancy occurs."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 16919