Yazid bin al-Asamm (may Allah have mercy on him) said: I went out with Sayyiduna Hasan (may Allah be pleased with him), and a slave girl was scraping some henna off his nails. Meanwhile a bundle of letters came to him, and he said: O slave girl, bring the basin. He poured water into it and threw the letters into the water; he did not open any of them, nor did he look at them. I said: O Abu Muhammad, from whom are these letters? He said: "From the people of Iraq, a people who neither return to the truth nor refrain from falsehood. Listen, I do not fear them for myself, but I fear them for that one," and he pointed to Sayyiduna Husayn.
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2678