It has been related in the book 'Al Irshadaat fi
ilm il Ibaadaat', that a man prayed for a dead woman
and this woman came in his dream to thank him and
assure him that his prayers had reached her in the
form of blessings.
It has been related in the book stated above that
a woman used to work in somebody's house. The owner
of the house had invited some guests and shortly after
the guests had left, the maid servant collected all
the remaining food and gave it as sadaqa in her mother's
name.
The next day the maid was visited by her sister who
informed her that she had dreamt their deceased mother
who informed her that the food her sister had sent
had reached her, but she had asked that the next time
she should send proper sadaqa and not remains of some
meals.
Sheikh Sudooq relates from Imam Jaffer Sadiq who
heard this tradition from the Holy Prophet Muhammad
(s.a.w.w.) that once Prophet Isa (a.s.) was passing
a grave whose occupant was being tortured. After some
time, Nabi Isa (a.s.) passed that grave again and
saw that the torture had stopped.
He asked Allah who revealed to him that the deceased's
son had given charity and so the torture had stopped.
(AL AMWAAT YATAKALLAMOONA MA'ANA)