The Messenger of Allah ﷺ came out to us with Hasan and Husayn, one on each of his shoulders. He kissed this one once and that one once, until he reached us.A man said to him, "Messenger of Allah, you truly love them."He replied, "Whoever loves them has loved me, and whoever hates them has hated me."
حدثنا ابن نمير قال أخبرنا حجاح يعني ابن دينار عن جعفر بن إياس عن عبد الرحمن بن مسعود
خرج علينا رسول الله ﷺ ومعه حسن وحسين هذا على عاتقه وهذا على عاتقه وهو يلثم هذا مرة ويلثم هذا مرة حتى انتهى إلينا فقال له رجل يا رسول الله إنك تحبهما فقال من أحبهما فقد أحبني ومن أبغضهما فقد أبغضني
Its isnad is hasan. Haythami said in 9/179, "Its narrators are trustworthy, though there is some disagreement about some of them." The hadith is found in Tabarani 3/40, no. 2649, and Bayhaqi 4/29, and Hakim 3/171, who graded it sahih, and Dhahabi agreed with him.