What is the ruling regarding someone who raises his hands for the takbir when he intends to prostrate after saying: "Rabbana wa lakal hamd (Our Lord, and to You be all praise)," believing that this is the place for raising them, and then hesitates about it? Is he required to perform the prostration of forgetfulness (sujud as-sahw)? Or is his prayer valid?

It is recommended to raise the hands in prayer in four places: when saying the opening Takbir (Takbirat al-Ihram), when bowing for Ruku', when rising from it, and when standing up for the third unit (rak'ah). It is not legislated to do so in other instances, such as when prostrating (hawi ila al-sujud). Raising the hands when descending for prostration out of forgetfulness does not invalidate the prayer nor does it necessitate the prostration of forgetfulness (sujud sahwi), just as an additional prostration of forgetfulness due to ignorance or forgetfulness does not invalidate the prayer. Your prayer is valid and does not need to be repeated.