The Messenger of Allah ﷺ said, "Whoever loves Hasan and Husayn has loved me, and whoever hates them has hated me."
حدثنا علي بن محمد حدثنا وكيع عن سفيان عن داود بن أبي عوف أبي الجحاف وكان مرضيا عن أبي حازم
قال رسول الله ﷺ من أحب الحسن والحسين فقد أحبني ومن أبغضهما فقد أبغضني
Sourcing, sahih. Nasai narrated it in al-Kubra, no. 8168, from the hadith of Sufyan Thawri, with this chain, and Busiri graded it sahih. It has sahih corroborating narrations recorded by Tabarani, Hakim, and others, and Hakim and Dhahabi graded some of them sahih.