Saeed bin Musayyib (may Allah have mercy on him) narrates that Umar bin Khattab (may Allah be pleased with him) said: "Beware lest you forget the verse of stoning, and (after a long time has passed) someone says, 'We do not find two prescribed punishments in the Qur'an.' The Messenger of Allah (ﷺ) carried out stoning, and we also stoned. By Him in Whose hand is my soul! If I were not afraid that people would say that Umar (may Allah be pleased with him) has added to the Book of Allah, I would have written it: 'When a married man and a married woman commit adultery, stone them both.' Indeed, we have recited this."
Hadith Referenceمسند الإمام الشافعي / كتاب الحدود / 1572
Hadith Takhrijاخرجه الترمذی - الحدود، باب ماجاء في تحقيق الرجم (1431) وقال حسن صحيح ومالك في الموطا، الحدود، باب ماجاء في الرجم واحمد (36/1 ، 43)۔