Sayyiduna Salman al-Farisi (may Allah be pleased with him) said: "The first of this Ummah to come to its Prophet (peace and blessings be upon him) will be the first of it to accept Islam: Sayyiduna Ali bin Abi Talib (may Allah be pleased with him)."
Hadith Referenceالمعجم الكبير للطبراني / باب السين / 6149