Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: Once Sayyiduna Umar (may Allah be pleased with him) was discussing with me about making a mistake in prayer. During this, Sayyiduna Abdur Rahman bin Awf (may Allah be pleased with him) came to us. He came and stayed with us. He said: I heard the Prophet (peace and blessings of Allah be upon him) say: "If a person has doubt about his prayer, then he should perform so much prayer that his doubt becomes about having added to the prayer."
Hadith Referenceسنن الدارقطني / كتاب الصلاة / 1415
Hadith Takhrij«أخرجه الضياء المقدسي فى ((الأحاديث المختارة))، 899، 900، والحاكم فى ((مستدركه)) برقم: 1215، 1217، والترمذي فى ((جامعه)) برقم: 398، وابن ماجه فى ((سننه)) برقم: 1209، والبيهقي فى((سننه الكبير)) برقم: 3875، والدارقطني فى ((سننه)) برقم: 1415 ، 1416 ، وأحمد فى ((مسنده)) برقم: 1678»