Sahih Muslim 1004cBook 25, Hadith 17
حَدَّثَنَا زُهَيْرُ بْنُ حَرْبٍ، حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ هِشَامِ بْنِ عُرْوَةَ، أَخْبَرَنِي أَبِي، عَنْ عَائِشَةَ، أَنَّ رَجُلاً، قَالَ لِلنَّبِيِّ صلى الله عليه وسلم إِنَّ أُمِّيَ افْتُلِتَتْ نَفْسُهَا وَإِنِّي أَظُنُّهَا لَوْ تَكَلَّمَتْ تَصَدَّقَتْ فَلِيَ أَجْرٌ أَنْ أَتَصَدَّقَ عَنْهَا قَالَ " نَعَمْ " .
My mother died all of a sudden, and I think if she (could have the opportunity) to speak she would have (made a will) regarding Sadaqa'. Will I be entitled to reward if I give charity on her behalf? He (the Holy Prophet) said: Yes.