It is an act of the Sunnah
that the person who received the charity should supplicate for the deceased that Allah (Exalted be He) may forgive him, and to say: "May Allah reward him well!" This is in accordance with the Hadith related by
Usamah ibn Zayd that he said: The Messenger of Allah (peace be upon him) said,
Anyone who received some good from someone and says to him "Jazak Allah khairan (May Allah reward you with the best)," has more than repaid him.
Al-Tirmidhy commented on this Hadith saying: This (Part No. 24; Page No. 227) is a Hasan (good) and Gharib (a Hadith with a single narrator usually at the beginning of the chain of narration) Hadith. However, it is better to abandon sayings, such as "We gave the deceased the reward of the charity, O Allah, make the reward of this charity reach him" on the part of those who eat the food offered in charity on behalf of the deceased. It is sufficient to intend that in your heart, rather than uttering such words. Allah (Exalted be He) says,
Say: "Will you inform Allâh of your religion
Allah (Exalted be He) knows everything, and nothing is hidden from Him, as He knows the intentions of His Servants and their aims according to which they are rewarded. Allah (Exalted be He) says,
...but if you conceal them, and give them to the poor, that is better for you.
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.