Hasan al-Basri narrated that he stayed with Sayyiduna Anas (may Allah be pleased with him) in Nishapur for two years, and during that time Sayyiduna Anas (may Allah be pleased with him) kept offering two rak'ahs each.
Imam al-Tabarani recorded it in al-Mu'jam al-Kabir, and its narrators have been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2959