Fatwa ID: 05118
Answered by: Maulana Shadman Ahmed
If the Muqtadi misses the sajdah tilawah with the imam and instead went into ruku (and only realized and got up when the imam got up), then is his salah valid?
In the name of Allah, the Most Gracious, the Most Merciful
Ruku is considered to be a substitute for sajdah for a person in prayer. The prayer will be valid if a Muqtadi were to make Ruku accidentally instead of making a SadjahTilawah. 
Only Allah knows best
Written by Maulana Shadman Ahmed
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Muḥammad Amīn `Ibn ’Abidīn, Radd al-Muḥtār ’Alā al-Durr al-Mukhtār, Vol. 2. Pg.106. vols. (Dār al-Fikr, 1252H); Abū al-Hasan Burhān al-Dīn ’Alī b. Abī Bakr b. ’Abd al-Jalīl al-Farghānī al-Marghinānī, al-Hidāyah fīsharḥ bidāyah al-Mubtadī, Vol. 1. Pg. 75. vols. (Beirut, Lebanon: Dār `Iḥyā al-Turāth al-’Arabiyyah, 593H).