Musnad Ahmad 2:195

'Abd al-Rahman narrated to us, Malik narrated to us, from al-Zuhri, from 'Ubayd Allah ibn 'Abd Allah, from Ibn 'Abbas, who said: 'Umar said: "Indeed, Allah the Exalted sent Muhammad, may Allah bless him and grant him peace, and revealed the Book to him. Among what He revealed to him was the verse of stoning (rajm). We recited it, understood it, and grasped it. I fear that a long time may pass for the people, and they will say: 'We do not find the verse of stoning in the Book of Allah,' and thus they will abandon an obligation that Allah has revealed. Indeed, stoning in the Book of Allah the Exalted is a truth against those who commit adultery if they have attained ihsan (marriage), from among men and women, when the evidence is established, or there is pregnancy, or confession."