Qays bin Abi Hazim says: Sayyiduna Sa'd bin Abi Waqqas (may Allah be pleased with him), while leading us in prayer, stood up after two rak'ahs. We said Subhan Allah for him, but he remained standing; he continued his standing until, when he finished the prayer, he said: "Did you think that I should have sat down? I did just as I saw the Prophet (peace and blessings be upon him) doing." Abu Uthman Amr bin Muhammad al-Naqid says: We have not heard anyone narrate this hadith as marfu' except Abu Mu'awiyah.
Abu Ya'la and al-Bazzar recorded it, and its narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2910