Simply replace the unfilled areas such as "" and "[date]" with your information.
Please allow me to inform [you/all of you/everyone/etc.] that I'm taking [a/#] [week/month] long leave of absence for [medical, personal, business, etc] reasons. [date], is the scheduled date of my leave and I am expected to be returning on [date], provided my [medical, personal, business, etc] period of time has gone well.
I know that the people I work with at [name of organization] will be more than able to take over my [role/tasks/etc] while I'm away. I thank [you/you all/etc.] in advance for your understanding and support during this time. I am relieved to know that everything will be left in good hands.
My best wishes to [you/all of you] and I look forward to seeing you soon.