It is narrated from Umm al-Mu'mineen Sayyidah Aisha (may Allah be pleased with her) that a man said to the Prophet Muhammad (peace and blessings be upon him): "My mother passed away suddenly. I think that if she had the opportunity to speak, she would have given some charity. If I give charity on her behalf, will she receive the reward?" The Prophet (peace and blessings be upon him) said: "Yes, she will receive it."
Hadith Referenceالسنن المأثورة / باب ما جاء في فدية الأذى / 505
Hadith Takhrijصحیح بخارى، الوصايا، باب ما يستحب لمن يتوفى فجأة ان يتصدقوا عنه، رقم: 2760، صحيح مسلم، الزكاة، باب وصول ثواب الصدقة عن الميت اليه، رقم: 1004