Giving Sadaqah on behalf of a dead person

There is/are hadith, Muslims are allowed to give sadaqah on behalf of a dead person if the money or treasure is sourced from money/treasure of that dead person.

In example. A father died. He leaved his money/treasure to his children. Then his children give that money/treasure to the poor as sadaqah on behalf of their father. Profit of a company that left by this dead person is also considered as sourced from this dead person treasure.

But currently, I do not find any reference Muslims can give sadaqah on behalf of a dead person if the money/treasure is absolutely not sourced from that dead person.

The scholars are agreed that the benefits of du’aa’, praying for forgiveness, giving charity and Hajj reach the deceased.

it was narrated in al-Saheehayn from ‘Aa’ishah that a man said to the Prophet (peace and blessings of Allaah be upon him): “My mother died suddenly and she did not leave a will, but I think that if she could have spoken she would have given in charity. Will she have a reward if I give in charity on her behalf?” The Prophet (peace and blessings of Allaah be upon him) said: “Yes.” Narrated by al-Bukhaari, no. 1388; Muslim, no. 1004.

And it was narrated by al-Bukhaari from Sa’d ibn ‘Ubaadah that his mother died when he was absent, and he said: “O Messenger of Allaah, my mother has died when I was absent. Will it benefit her if I give in charity on her behalf?” He said: “Yes.” He said: “I ask you to bear witness that my garden that bears fruit is given in charity on her behalf.” Narrated by al-Bukhaari, 2756.


http://www.islamqa.com/en/ref/42384