Musnad Ahmad 302
It was narrated from Sa’eed bin al-Musayyab that `Umar bin al-Khattab رضي الله عنه said:
Beware of overlooking the verse of stoning and (do not let) anyone say: “We do not find two hadd punishments in the Book of Allah, for I saw the Messenger of Allah (ﷺ) stone [adulterers] and we stoned [them] after he was gone.
حَدَّثَنَا يَزِيدُ، أَنْبَأَنَا يَحْيَى، عَنْ سَعِيدِ بْنِ الْمُسَيَّبِ، أَنَّ عُمَرَ بْنَ الْخَطَّابِ، رَضِيَ اللَّهُ عَنْهُ قَالَ إِيَّاكُمْ أَنْ تَهْلِكُوا عَنْ آيَةِ الرَّجْمِ وَأَنْ يَقُولَ قَائِلٌ لَا نَجِدُ حَدَّيْنِ فِي كِتَابِ اللَّهِ تَعَالَى فَقَدْ رَأَيْتُ رَسُولَ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ رَجَمَ وَرَجَمْنَا بَعْدَهُ‏.‏