Laws Of Salah :
Double The Reward
We all know that performing Wuzu is hard when it's cold or when we are tired or suffer from flu, headache or any other illness, but if someone does succeed in performing Wuzu in a state of difficulty then according to Hadith he will rewarded twice as much.
(mulakhkhasan al mu'jamul awsat, V4 , P106, Hadith 5366, dar-ul-Kutubul Ilmiyyah Beirut)