Umar bin Khattab performed the Hajj and intended to deliver a sermon to the people.Abdul-Rahman bin Awf said to him, "The common rabble of people have gathered around you, so postpone it until you reach Madinah."When he arrived in Madinah, I drew close to him near the pulpit and heard him say, "Some people are saying, 'What is this stoning? The Book of Allah only mentions lashing.' Yet the Messenger of Allah ﷺ carried out stoning, and we carried it out after him. Were it not that people would say I added to the Book of Allah what is not in it, I would have written it down as it was revealed."
حدثنا محمد بن جعفر وحجاج قالا حدثنا شعبة عن سعد بن إبراهيم قال سمعت عبيد الله بن عبد الله بن عتبة يحدث عن ابن عباس
حج عمر بن الخطاب رضي الله عنه فأراد أن يخطب الناس خطبة فقال عبد الرحمن بن عوف إنه قد اجتمع عندك رعاع الناس فأخر ذلك حتى تأتي المدينة فلما قدم المدينة دنوت منه قريبا من المنبر فسمعته يقول وإن ناسا يقولون ما بال الرجم وإنما في كتاب الله الجلد وقد رجم رسول الله ﷺ ورجمنا بعده ولولا أن يقولوا أثبت في كتاب الله ما ليس فيه لأثبتها كما أنزلت
Its isnad is sahih. Hajjaj is Ibn Muhammad Masissi. The hadith will come at greater length at 391, and see also 276, 331.