The RAM spec for your model is 1333MHz DDR3 PC3-10600. Unlike pre-2006 Macs that would happily clock back faster RAM to work on a slower bus, your Macbook Pro may be very unhappy with too-fast RAM. Use the right RAM.
Most senior contributors here, having seen thousands of problem posts about serious issues with inexpensive RAM, recommend ONLY Crucial or OWC RAM. Leroy has given you the Crucial link. This is the OWC link.:
https://eshop.macsales.com/shop/memory/Apple_MacBook_MacBook_Pro/Upgrade/DDR3_1333MHz_SDRAM
RAM is best installed in matched pairs, so this two-module "kit" is what I used to upgrade my 2012 MBP13 to 8GB:
https://eshop.macsales.com/item/OWC/1333DDR3S08S/
My computer has never shown being needy for RAM with 8GB.
NOTE: Adding RAM will NOT make your computer detectibly faster in actual use. Only adding a solid-state drive (SSD_ will. Here is real launch time data from two big apps on my Macbook Pro 13 that show what happened when I first doubled the RAM, then upgraded to an SSD:
Base system as shipped:
4GB RAM and slow SATA 3GBps 5400rpm hard drive: Office 2008 and Photoshop Elements took 15-18 seconds to be ready to use.
First upgrade, double the RAM:
8GB RAM and slow SATA 3GBps 5400rpm hard drive: Office and Photoshop Elements took 15-18 seconds to be ready to use.
Second upgrade, inexpensive solid-state drive:
8GB RAM and fast SATA 6GBps SSD: Office and Photoshop Elements take under 4 seconds to be ready to use.