Musnad Ahmad 551:25

Hashim narrated to us, he said: Al-Faraj narrated to us, from Rabi'ah ibn Yazid, from Uqbah ibn Amir, from the Prophet, may Allah bless him and grant him peace, the like of it, except that he said: "If you exert effort and hit the correct judgment, you have ten rewards. And if you exert effort and miss, you have one reward."