On the day of Eid al-Fitr, Imam Ali bin Abi Talib (as) delivered a sermon in which he said:

"O people! Verily this day of yours is the day when the righteous are awarded and the wretched are losers. It is a day which is similar to the one on which you shall be standing (before your Lord). Therefore, when you come out of your homes to go to places of your prayer, remind yourselves about the day when you (your souls) shall come out of your bodies to go to your Lord. When you stand on places of your prayer, remind yourselves of your standing in presence of your Lord (on the day of Judgment). And when you return to your homes (after prayer), remind yourselves about your returning to your homes in Paradise.
O Servants of Allah! Verily the minimum reward for those men and women who fasted (during Ramadhan), is an Angel, who calls out to them on the last day of the month of Ramadhan (saying): O Servants of Allah! Rejoice the Glad Tiding that all your previous sins have been forgiven . Therefore, watch out in those things which serve as your re-creation (on this day and days to follow)"

In his book of man-la-yahzuruhul-faqih, Shaykh al-Saduq has reported the following sermon from Imam 'Ali Amir al-Mu'minin, peace be upon him.