The angel called Shomer Dapim:
The angel called Shomer Dapim stands by the Sefarim and supervises that they are treated respectfully. There was once an individual who ended his daily writing in a Sefer with a verse that has a negative connotation. The next day when he entered his study, he saw a frightening looking individual sitting on his chair and reading his Sefer. He told the individual that he is the angel called Shomer Dapin and he supervises the pages of Sefarim, and when one concludes with an evil verse, he can cause the writer potential harm. That individual happened to be a Tzaddik and he made a deal with the angel not to hurt him, in exchange for that he will not continue writing in that Sefer until Shavuos, and so it was.
 Brought in Siddur Arizal of Maharik; Chosen Yeshuos 27:3 [on Yeshuos Chochma 27]