It is narrated from Sayyiduna Wathilah bin al-Asqa' (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "You will remain in goodness as long as there remains among you one who saw one who saw me and kept my company."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18427