Tawus (may Allah have mercy on him) narrates from Sayyiduna Wathilah (may Allah be pleased with him) that he said: I said: "O Prophet of Allah, tell me." He (peace and blessings be upon him) said: "If you wish, I will tell you what you have come to ask about, and if you wish, ask yourself." I said: "Rather, you tell me, O Messenger of Allah, for that is more pleasing to my heart." He (peace and blessings be upon him) said: "You have come to ask about certainty and doubt." I said: "That is it, O Messenger of Allah." He (peace and blessings be upon him) said: "Certainty is what settles in the heart and with which the heart is at rest, even if a mufti gives you a fatwa. Leave what makes you doubt for what does not make you doubt, for goodness lies in tranquillity and doubt lies in unease; and when you are in doubt, leave what makes you doubt for what does not make you doubt." I said: "O Prophet of Allah, may my father and mother be ransomed for you, what is tribalism ('asabiyyah)?" He (peace and blessings be upon him) said: "That you help your people in wrongdoing; and the scrupulous one is he who stops at doubtful matters; and the one greedy for the world is he who seeks it by unlawful means; and sin is what pricks at the heart."
Hadith Referenceالمعجم الكبير للطبراني / باب الواو / 18417