The word Salaf is a shortened version of the word 'Salaf as-Saalih', which means the 'Righteous Predecessors'.
It refers specifically to the first three generations of Islaam in which the Prophet Muhammad (صلى الله عليه وسلم) described as being the best generations of Muslims. The first, the Prophet (صلى الله عليه وسلم) and his Sahaabah (companions). The second, the Taabi'een (the followers of the companions). The third, the Tabaa'at-Taabi'een (the followers of the followers of the companions).
UMAR (radiallaahu anhu) became unconscious after he was stabbed, and it was said: “Nothing would wake him up except the call to prayer, if he is still alive.” They said to him, “The prayer has finished, O Leader of the Believers!” He woke up and said, “The prayer, by Allah! Verily, there is no share in Islam for whoever abandons the prayer.” He performed the prayer while his wound was bleeding. (Sifat As-Safwah 2/131, As-Siyar 5/220)