This short guide describes how to install PHP 7 on a Raspberry Pi running Raspbian Linux as operating system.

Edit the apt sources list, /etc/apt/sources.list
sudo nano /etc/apt/sources.list

Add the following lines to the file:

deb http://repozytorium.mati75.eu/raspbian jessie-backports main contrib non-free
#deb-src http://repozytorium.mati75.eu/raspbian jessie-backports main contrib non-free

Run the following commands in the terminal. You need superuser (root) access.

su
gpg --keyserver pgpkeys.mit.edu --recv-key CCD91D6111A06851
gpg --armor --export CCD91D6111A06851 | sudo apt-key add -
apt-get update
apt-get install php7.0 php7.0-curl php7.0-gd php7.0-imap php7.0-json php7.0-mcrypt php7.0-mysql php7.0-opcache php7.0-xmlrpc

And if you want to install Apache 2 + mod_php:
apt-get install apache2 libapache2-mod-php7.0