[By this letter you will learn how to write a permission letter to principal to attend class without book. You can modify these formats as your requirement.]
Sub: Application for Permission to Attend Class without Book
Sir, I have misplaced my course of your subject in the cafeteria yesterday. This morning I have posted it in the official Facebook group of the university and I am hoping to hear any good news soon. (show your actual problem and situation). But it might take a few days and it was so expensive I cannot afford to buy another one. I want a permission letter from you that you can allow my entrance in class without the book for two to three days.
Until then I will make notes of the lecture and you will not find a complaint regarding my assignments and quizzes. I hope you will understand my problem and will grant me the permission.
Your honorary student,