Sayyiduna Ammar bin Yasir (may Allah be pleased with him) narrates: The Prophet (peace and blessings be upon him) said: "I enjoin whoever believes in me and affirms me as truthful to hold wala' (that is, loyal friendship) towards Ali bin Abi Talib. Whoever holds wala' towards him holds wala' towards me, and whoever holds wala' towards me holds wala' towards Allah Almighty. Whoever loves him loves me, and whoever loves me loves Allah Almighty. Whoever hates him hates me, and whoever hates me hates Allah Almighty."
Al-Tabarani recorded it with two chains; the better of them contains a group of da'if (weak) narrators who have also been declared trustworthy.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب المناقب / 14640