assalamou'alaikum wa rehmatullahi wa barakaat.
It was the Sunnah of the Prophet (sallallahu 'alahi wassallam) to make the following du'a in the witr salaat:
"...Bless me in what You have given me. And avert and turn away from me the evil that hads been decreed for me, for verily Yiu decre (all things) and none can decree against You..."Reported by At-Tirmidhi