It is narrated from Amr bin Al-Aas (may Allah be pleased with him) that he heard the Messenger of Allah (ﷺ) saying: "When a ruler exercises ijtihad (independent judgment) and his decision is correct, he will have a double reward; and when a ruler exercises ijtihad and makes a mistake, he will have a single reward."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1685
Hadith Takhrijاخرجه البخاري، الاعتصام بالكتاب والسنة، باب اجر الحاكم اذا اجتهد فأصاب أو اخطا (7352) ۔ ومسلم، الأقضية، باب بیان اجر الحاكم اذا اجتهد، فأصاب أو أخطا (1716)۔
Abdul Aziz bin Muhammad narrated to us from Yazid bin Hadi, he said: I narrated this hadith to Abu Bakr bin Muhammad bin Amr bin Hazm, so he said: "Abu Salamah bin Abdur Rahman narrated to me from Abu Hurairah (may Allah be pleased with him) in the same manner."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1686
It is narrated from Amr bin Al-Aas (may Allah be pleased with him) that he heard the Messenger of Allah (ﷺ) saying: "When a ruler makes a judgment by ijtihad and is correct, he will have a double reward, and when a ruler makes a judgment by ijtihad and errs, he will have a single reward."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1687
Yazid bin Hād said: "I narrated this hadith to Abu Bakr bin Muhammad bin Amr bin Hazm, so he said that Abu Salamah narrated this hadith to me in the same way from Abu Hurairah (may Allah be pleased with him)."
Hadith Referenceمسند الإمام الشافعي / كتاب القضاء والأحكام والدعاوى والبينات واليمين ومع الشاهد والأيمان والشهادات / 1688