Sayyiduna Samurah (may Allah be pleased with him) states: The Prophet (peace and blessings be upon him) forbade sitting in the manner of tawarruk and iq'a' during the prayer, and sitting on the heels with both feet upright.
Bazzar recorded it, and Tabarani recorded it in al-Mu'jam al-Awsat; its chain contains Sa'id bin Bashir, about whom there is criticism.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الصلاة / 2468