Reference: http://mufti.af.org.sa/ar/content/البسملة-عند-الطعام
Question: What should the Muslim say if he forgets to utter [بسم الله] when doing wudhoo, and then he remembers [not having done so] just before completing the wudhoo? Should he utter [بسم الله في أوله و آخره] just as he would when eating, or how would you advise?
Response: Uttering [بسم الله] when doing wudhoo is obligatory should one remember [to do so]. If however he forgets [to do so] at the beginning of the wudhoo, then he can utter it at any stage he remembers [during the wudhoo].
