Hadith.1005 – Zurarah narrated from one of the Imams that He said
"Indeed, Allah (swt), Blessed and Exalted, has made ruku' (bowing) and Sujood (prostration) obligatory, while recitation is a Sunnah. Whoever intentionally leaves out the recitation must repeat the prayer, but if someone forgets, there is no fault upon them."