We should give charity for Imam Mehdi. You might ask if Imam Mehdi needs us to give charity for him?! Who are we to give charity for someone like Imam Mehdi?! This is very right. He does not at all need our charity or prayers, and these are what we need to do for ourselves. It is actually possible that our charity or prayers do have an effect and because of those, God takes away some sorrow or dangers from him or his family. There is nothing that could deny this fact. We should not appoint one day in a week only for paying charity and we need to give charity for Imam Mehdi every morning that we leave home and every night that we come back home, as much as we could. This will bring us lots of bounties.

In general, giving charity has different effects that show the honesty of a believer’s faith. By giving charity people could prove how honest they are in their faith towards God. It will also help satisfy the needs of the believers and establish welfare, as Qur’an says in Verse 103 of Al Tawbah Surah,
“Of their goods, take alms, that so thou mightest purify and sanctify them; and pray on their behalf. Verily thy prayers are a source of security for them: And God is One Who heareth and knoweth.”‌

Source: Tebyan