All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
It is a Sunnah for whoever wants to go to sleep to dust off his bed with the extremity of his Izaar (lower garment) or Qamees/Thawb (body-length garment), but we have not come across a text that states that he dusts it directly with his right hand. The evidence about this is what Abu Hurayrah narrated that the Prophet said: "When one of you goes to his bed, let him dust off his bed with inner extremity of his lower garment, for he does not know what came onto it after he left it. Then let him say: In Your name, my Lord, I lie down, and in Your name I rise. If You take my soul, then have mercy on it, and if You return it, then protect it as You protect Your righteous slaves.” [Al-Bukhari]
The scholars explained the wisdom behind the order to dust one's bed with the inner extremity of his lower garment as they said: “So that the outside of the lower garment would remain clean. The Hadeeth explained the reason for the order with the Prophet’s saying: “He does not know what came onto it after he left it," meaning a snake or a scorpion or otherwise..."
For more benefit on the etiquette of going to sleep in general, please refer to Fatwa 90183.
Allaah Knows best.