Free Hi-Res Mockup PSD (3579 x 2386 px)
Free Hi-Res Mockup PSD (3579 x 2386 px) is a free Mockup design resource made by Dribbble user Karolina Grabowska. As far as I can tell, its license is Free for Commercial and Personal Purposes.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.