These books cite a tradition narrated by Abu Abdullah Imam...

These books cite a tradition narrated by Abu Abdullah Imam Ja’far al-Sadiq (as) in which the Imam (as) says, "The Messenger of Allah (S) appointed only (Imam) Ali (as) as his successor, while (Imam) Ali (as) assigned Imamate to both (his sons) al-Hassan and al-Husayn (as). When al-Hassan (as) was the Imam, a man entered on the day of Arafat and saw al-Hassan (as) eating his lunch while al-Husayn (as) was fasting.

The same man came to see al-Husayn (as) when he became the Imam following the death of (Imam) al-Hassan (as), also on the Arafat day, and he saw him eating while his son (Imam) Ali son of al-Husayn (Zainul-’Abidin [as]) was fasting.

The man (apparently quite confused) asked (Imam) al-Husayn (as), ‘Why is it that I visited al-Hassan (as) and found him eating while you yourself were fasting, and now I visit you and find you not fasting (while your son is)?!' (Imam) al-Husayn (as) said, ‘Al-Hassan was then the Imam; he did not fast for fear his fast would be regarded as a Sunnah followed by people. When he died and I became the Imam, I did…