Shmiras Halashon / Ch. 3, 4 – 121

Our Sages said, ‘A person should preserve what he learns so he won’t be ashamed in the day of judgement. When he is told to present the Torah he learned etc.’ They also said that if a person forgot something he learned through no fault of his, an angel comes and teaches it to him to spare him the humiliation. For this reason alone, a person should be very careful not to interrupt his Torah learning with other things. Besides being forbidden, it will be very embarrassing. If offered to buy a beautiful tome of Talmud with whole pages of story books bound together in it, no one would buy it. And so it is with his learning, when the angels will present what he learned it will be filled with stories and nonsense, and he will be mortified. Therefore a person should be careful that his learning be pure without any extraneous speech.