Is saying the Shahada before sleep considered a Bid'ah (innovation) because it is not mentioned in the books of Adhkar (remembrances)?

There is no innovation (bid'ah) in reciting the Shahada (testimony of faith) before sleep, for remembrance (dhikr) is commanded to be increased at all times and in all circumstances. Allah has urged its abundance and made success dependent upon it. Therefore, there is no harm in uttering the Shahada before sleep or at any time, as long as there is no commitment to a specific time or a fixed number.