1. Muslims are to follow the explicit injunctions and commandments in accordance with the Quran
2. Sunnah are the habits, day-to-day activities, and event specific instructions of the prophet to his companions during his lifetime.
3. Ahadiths are the stories and Islamic/Arab folk lores associated with the Holy prophet. These sayings (verbal form) were passed on from generation to generation, and written some 200 years later by several Imams who were on the Abbasid payroll.
4. Quran specifically forbids to follow anything outside of the Quran.
Namaz is physically an exact copy of the Zoroastrian prayer including the timing and cleanliness requirements. It was already an established form of prayer.
N2 Islamists have conveniently and wrongfully translated "Establishing Salat" to Namaz.