What can we do for those who have passed away?
Let me begin by saying that "Every soul shall have a taste of death: And only on the Day of Judgment shall you be paid your full recompense. "(3:185)
We have to accept this fact & recognise how short is our life.We must pray for the deceased forgiveness.
I)Whom can we pray for?
"And Abraham prayed for his father's forgiveness only because of a promise he had made to him. But when it became clear to him that he was an enemy to God, he dissociated himself from him: for Abraham was most tender-hearted, forbearing."(9:114)
When a person does not die in a state of Islam,then we are not allowed to pray for them.
II)What should we do for the dead?
a)Sadqa
SAHIH BUKHARI,Volume 4, Book 51, Number 19:
Narrated Ibn 'Abbas:
The mother of Sad bin 'Ubada died in his absence. He said, "O Allah's Apostle! My mother died in my absence; will it be of any benefit for her if I give Sadaqa on her behalf?" The Prophet said, "Yes," Sad said, "I make you a witness that I gave my garden called Al Makhraf in charity on her behalf."
b)Complete fast
Book 006, Number 2555:
Ibn 'Abbas (Allah be pleased with them) reported: A man came to the Apostle of Allah (may peace be upon him) and said: Messenger of Allah, my mother has died (in a state) that she had to observe fasts of a month (of Ramadan). Should I complete (them) on her behalf? thereupon he (the Holy Prophet) said: Would you not pay the debt if your mother had died (without paying it)? He said: Yes. He (the Holy Prophet) said: The debt of Allah deserves more that it should he paid.
III)What should't do for the dead?
SAHIH BUKHARI,Volume 2, Book 23, Number 377:
Narrated Abu Burda:
That his father said, "When Umar was stabbed, Suhaib started crying: O my brother! 'Umar said, 'Don't you know that the Prophet said: The deceased is tortured for the weeping of the living'?"