This is a notice of raise. So the raise has been approved. You can mention that their request has been approved but sometimes there doesn't even have to be a request. You can give an employee a raise without them asking for it. So here is what you say.
Subject Line: Notice of Raise
Dear [Title and Name of Recipient],
It's my pleasure to inform you that we have determined that your excellent work for us is worthy of a raise in salary.
We are extremely pleased with the way in which you have conducted yourself and provided value for this company over ther last [time period], we'd like to show our appreciation in financial rewards.
From [data], your new salary shall be [salary].
Congratulations and keep up the great work!
Best regards,
[Full Name]