Imam Sadiq (as): Imam Hassan (as) said in presence of Holy Prophet (sw) what is the reward of some one who visit you, the Holy Prophet replied any one visits me or your father (Imam Ali a.s) it will be right of Allah swt to visit him in day of Qiyamat and rescue him from his sins.
Abi Wahab Basri said I entered to the Madinah then I visited Imam Sadiq (as) and I said may my I sacrifice my life for you I visiting you but could not visit Imam Ali (as) Shrine, Imam said worse thing you have done, if you were not our shia I would not look at you, would not you like to visit whom Allah swt visit him with angels, and All Prophets visit him with believers I said may I sacrifice myself for you I didn’t know that Imam said be aware that the position of Imam Ali (as) with Allah swt is better than all other Imams and for first Imam is rewards of all other Imams actions so He will be superior on the bases of all their actions. (Ref: Kamil Al-Ziyarat)