Sa'id bin al-Musayyib (may Allah have mercy on him) said that Sayyiduna Umar (may Allah be pleased with him) said: The Prophet (peace and blessings be upon him), Sayyiduna Abu Bakr (may Allah be pleased with him) and I have carried out stoning. By Allah, had I not feared that I would be adding to the Book of Allah, I would have written it in the Mushaf; and I fear that peoples will come who will not find it in the Qur'an and so will not believe in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحدود / 16922