Sayyiduna Ibn Abbas (may Allah be pleased with them both) said concerning this saying of Allah Almighty, "The Most Merciful will appoint for them affection" [Maryam: 96]: "It is (placing) love in the hearts of the believers. It was revealed concerning Ali bin Abi Talib (may Allah be pleased with him)."
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 12601