Questioner: If someone forgot to say “bismillāh” at the start of his wuḍū [ablution], what is binding upon him?
Shaikh Al-Albānī: Nothing. [Allāh says:]
O our Lord, do not hold it against us if we [leave an obligation or do something prohibited because we] forgot, or [if] we do something the wrong way [because we were ignorant about the correct Islāmic way to do it].¹
¹Extract from Al-Baqarah 286, English meaning based on Tafsīr Ibn Kathīr
Silsilah Al-Hudá wa-l-Nūr, 051.