Muhammad bin Sirin said: I was informed that a funeral passed by Sayyiduna al-Hasan bin Ali and Sayyiduna Ibn Abbas (may Allah be pleased with them both). Sayyiduna al-Hasan stood up and Sayyiduna Ibn Abbas sat. Sayyiduna al-Hasan said to Sayyiduna Ibn Abbas: "Did you not see that a funeral passed by the Prophet (peace and blessings be upon him) and he stood?" He said: "Yes indeed, and then he sat."
Hadith Referenceالمعجم الكبير للطبراني / باب الحاء / 2733