What is Sheikh Muhammad Hassan's evidence that not raising the hands in prayer is considered a mistake?

If the questioner, by "not raising" in prayer, means not raising the hands before bowing and after rising from it, then raising the hands in these positions is a confirmed Sunnah, established by the Prophet, peace and blessings be upon him, through continuous and widely transmitted traditions (Mutawatir Sunnah). Al-Bukhari narrated from Ibn Umar, may Allah be pleased with them both, that the Prophet, peace and blessings be upon him, would raise his hands to the level of his shoulders when saying the opening Takbir (Takbirat al-Ihram), when saying the Takbir for bowing, and when rising from it. Imam Ibn al-Qayyim stated that raising the hands in these three positions was narrated by about thirty individuals, and the ten promised Paradise all agreed on narrating it, and nothing contrary to that was authentically reported from the Prophet, peace and blessings be upon him. Based on this, abandoning the raising of hands in these positions is considered contrary to the Sunnah.