Sayyiduna Abu Hurairah (may Allah be pleased with him) narrates that the Noble Prophet (peace and blessings be upon him) said: "When a person who makes judgments exercises ijtihad (independent reasoning) and gives a correct judgment, he receives two rewards, and when he exercises ijtihad and makes a mistake in his judgment, he receives one reward." In another narration, the words are: "When a judge exercises ijtihad while making a judgment and gives a correct judgment, he receives two rewards, and when he makes a mistake while making a judgment, he receives one reward."
Hadith Referenceسنن الدارقطني / كتاب فى الأقضية والأحكام وغير ذلك / 4464
Hadith Takhrij«أخرجه البخاري فى ((صحيحه)) برقم: 7352 م، ومسلم فى ((صحيحه)) برقم: 1716، وابن حبان فى ((صحيحه)) برقم: 5060،وأبو داود فى ((سننه)) برقم: 3574، والترمذي فى ((جامعه)) برقم: 1326، وابن ماجه فى ((سننه)) برقم: 2314،والدارقطني فى ((سننه)) برقم: 4460، 4464، 4478، 4479، 4480، 4481، وأحمد فى ((مسنده)) برقم: 18052»