The Messenger of Allah ﷺ said, "Whoever loves these two has loved me, and whoever hates them has hated me," meaning Hasan and Husayn.
حدثنا أبو أحمد حدثنا سفيان عن أبي الجحاف عن أبي حازم
قال رسول الله ﷺ من أحبهما فقد أحبني ومن أبغضهما فقد أبغضني يعني حسنا وحسينا
Its isnad is sahih. Abu Ahmad is Zubayri, Muhammad bin Abdullah bin Zubayr Asadi. Sufyan is Thawri. Abu Jahhaf, with the jim vowelled fatha and the plain ha doubled, and ending in fa, is Dawud bin Abu Awf Tamimi, and he is trustworthy. Ibn Abu Hatim reported from Sufyan that he used to consider him trustworthy and hold him in high regard. Bukhari reported in al-Kabir from Sufyan, who said, "Abu Jahhaf narrated to us, and he was well regarded." Ahmad and others also considered him trustworthy. Bukhari gave his biography at 213/1/2, Ibn Saad at 6:228, and Ibn Abu Hatim at 1/2/421–422.The word "marziyyan" (well regarded) in Sufyan's statement appears in al-Tahdhib as "murjian" (a Murjiite), which is a corruption. The correct reading was established in its margin, quoting from al-Tahdhib al-Kabir of Mizzi. Likewise, the correct reading is found in Sunan Tirmidhi 1:186 with our commentary, and likewise in a reliable manuscript copy of Nasb Raya.The hadith was narrated by Ibn Majah at 143, by way of Waki from Sufyan, with the wording, "Whoever loves Hasan and Husayn..." and so on. Busiri said in his Zawaid, "Its isnad is sahih, its men are trustworthy."It will also come again at 9758, from the narration of Waki from Sufyan, in shortened form, with the wording, "O Allah, I love him, so love him." See 2406, 7392.