Sunan an Nasai
3991
Sahih+2

It was narrated that 'Abdullah said:"The Messenger of Allah [SAW] said: 'The first thing concerning which a person will be brought to account will be the Salah, and the first thing concerning which scores will be settled among the people, will be bloodshed

SahihAbu Ghuddah
SahihAl-Albani