Salah is an `Ibadah (worship) that is Tawqifiy (bound by a religious text and not amenable to personal opinion). The Hadith Qudsy, though being a Wahy (revelation) from Allah, are not the same as Qur'an. Allah (Exalted be He) commands His Slaves through His Prophet's words and actions (peace be upon him) to recite the Qur'an, not the Qudsy or prophetic Hadith in Salah. Allah did not make it incumbent upon His Slaves to recite them instead of Al-Fatihah or the Surah that follows it. Also, there is no evidence in the Qur'an or the Sunnah indicating that whatever was revealed from Allah should be recited in Salah, otherwise the prophetic Hadith would have been recited in it. All these matters are Tawqify and not subject to Ijtihad (juristic effort to infer expert legal rulings), Ta`lil (logical and methodical reasoning), or personal opinions.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.