When and how does one dust the bedding three times?

Al-Bukhari and Muslim narrated from Abu Hurayrah (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When one of you goes to his bed, let him dust off his bed with the inside of his lower garment, for he does not know what might have come onto it after him. Then let him say: 'In Your Name, my Lord, I lay my side down, and in Your Name, I raise it. If You take my soul, then have mercy on it, and if You release it, then protect it with what You protect Your righteous servants.'"

Al-Nawawi said: "It is recommended to dust off one's bed before entering it, lest there be a snake, scorpion, or other harmful creatures in it. And let him dust it off with his hand covered by the edge of his lower garment, so that he does not encounter anything disliked if there is something there."

Accordingly, dusting off the bed should be done when one intends to sleep, and it should be done with the edge of one's garment or something similar.