The Messenger of Allah ﷺ said, "Whoever loves Hasan and Husayn has loved me, and whoever hates them has hated me."
قال رسول الله ﷺ: من أحب الحسن والحسين فقد أحبني، ومن أبغضهما فقد أبغضني.
Nasai narrated it in al-Kubra (8112), Ibn Majah (143), and Ahmad (7876), all through the route of Sufyan Thawri, from Abu Jahhaf Dawud bin Abu Awf, from Abu Hazim, from Abu Hurairah, who mentioned it.Its isnad is hasan because of Abu Jahhaf, for his hadith is hasan despite his extremism in his Shiism, but he has been corroborated. He was corroborated by Salim bin Abu Hafsa Ajli, from Abu Hazim, who said,"I was a witness on the day Hasan bin Ali died, and I saw Husayn bin Ali saying to Saeed bin Aas, while poking him in the neck, 'Go ahead.' He said, 'Were it not that it is the practice, I would not have put you forward.' There was something between them. So Abu Hurairah said, 'Do you begrudge the son of your Prophet ﷺ a piece of ground in which to bury him, when I heard the Messenger of Allah ﷺ say...'" and he related the hadith.Ahmad narrated it (10872), and Abu Yaala (6215), and Hakim graded it sahih (3/171), though no one mentioned this story except Hakim. Abu Jahhaf has other corroborating narrations as well.