Silsilah as-Sahihah 311 — Single report is proof even in beliefs

Sayyiduna Anas (may Allah be pleased with him) narrates that some people from Yemen came to the Messenger of Allah (peace and blessings be upon him) and said: "Send with us a man who will teach us the Sunnah and Islam." He took hold of the hand of Sayyiduna Abu Ubaidah (may Allah be pleased with him) and said: "He is the trustworthy one of this Ummah."