Question: If he forgets the adhkaar, for example the adkhar for the washroom, does he say it when he remembers?
Answer: “He does not recite it because it is a Sunnah whose place was missed. However, if you remember it close to the time then there is no harm”.
[Kanz uth-Thameen Fi Su’alaat Ibn Sunayd no. 748 pg. 175]
Faisal Ibn Abdul Qaadir Ibn Hassan