Found the following hamletworks.org entries referring to line 300

View Commentary Note for 300
300 Quee. Let not thy mother loose her prayers Hamlet, 1.2.118

View Immaterial Textual Note for 300
300 Quee. Let not thy mother loose her prayers Hamlet, 1.2.118

View Material Textual Note for 300
300 Quee. Let not thy mother loose her prayers Hamlet, 1.2.118