بِسْمِ الله/ بِسْمِ اللهِ في أَوَّلِهِ وَآخِـرِه
Bismillaah./ Bismillaahifee awwalihi wa aakhirihi.
With the Name of Allah.
And if you forget then when you remember, say:
With the Name of Allah, in the beginning, and in the end.
Reference: Abu Dawud 3/347, At-Tirmithi 4/288. See Al- Albani s Sahih At-Tirmithi 2/167.