Musannaf Ibn Abi Shayba 28:1020

'Abd al-A'la narrated to us, from Ma'mar, from al-Zuhri, who said: They used to place bets during the time of the Messenger of Allah, may Allah bless him and grant him peace. Al-Zuhri said: And the first one to give [a prize] for it was 'Umar ibn al-Khattab.