If before bending for rukūʿ one realises that he has not recited Sūrat al-Ḥamd and the other surah, he must recite them. If he realises that he has [recited Sūrat al-Ḥamd but] not the other surah, he must recite only the other surah. However, if he realises that he has not recited Sūrat al-Ḥamd only, he must first recite Sūrat al-Ḥamd and then the other surah again.
Similarly, if one bends forward but before getting into the rukūʿ position he realises that he has not recited Sūrat al-Ḥamd and the other surah, or only the other surah, or only Sūrat al-Ḥamd, he must stand up straight and act according to what has been mentioned earlier in this ruling.