Question: Assalamu alaikum,
Is it permissible to give your wealth (i.e. cash), as charity, on the behalf of someone else?

Answer: Wa alaikum assalam wa rahmatullahi wa barakatuh,

I pray that you are in the best of health and faith, insha’Allah.

Yes, a person may designate the reward of any voluntary good deed to another person, whether the recipient is alive or deceased. [Ibn `Abidin, Radd al-Muhtar]
A man told the Prophet (peace and blessings be upon him) that his mother died a sudden death and did not have a chance to leave a bequest in her will, and that were she able to speak she would want to donate charity. He then asked if the reward of charity on behalf of his deceased mother would reach her, to which the Prophet (peace and blessings be upon him) replied, “Yes.” [Muslim]

Nawawi comments, “this tradition (hadith) shows us that charity benefits the deceased, and its reward reaches them; and it is thus according to the consensus of the scholars…” [Nawawi, Sharh Sahih Muslim]
For a detailed response, please see: Donating Reward to the Dead: A Detailed Answer
And Allah alone gives success.

في الدر المختار: الاصل أن كل من أتى بعبادة ما له جعل ثوابها لغيره وإن نواها عند الفعل لنفسه لظاهر الادلة.… (العبادة المالية) كزكاة وكفارة (تقبل النيابة) عن المكلف (مطلقا)
في رد المحتار: مَطْلَبٌ فِي الْقِرَاءَةِ لِلْمَيِّتِ وَإِهْدَاءُ ثَوَابِهَا لَهُ [ تَنْبِيهٌ ] صَرَّحَ عُلَمَاؤُنَا فِي بَابِ الْحَجِّ عَنْ الْغَيْرِ بِأَنَّ لِلْإِنْسَانِ أَنْ يَجْعَلَ ثَوَابَ عَمَلِهِ لِغَيْرِهِ صَلَاةً أَوْ صَوْمًا أَوْ صَدَقَةً أَوْ غَيْرَهَا كَذَا فِي الْهِدَايَةِ ، بَلْ فِي زَكَاةِ التَّتَارْخَانِيَّة عَنْ الْمُحِيطِ : الْأَفْضَلُ لِمَنْ يَتَصَدَّقُ نَفْلًا أَنْ يَنْوِيَ لِجَمِيعِ الْمُؤْمِنِينَ وَالْمُؤْمِنَاتِ لِأَنَّهَا تَصِلُ إلَيْهِمْ وَلَا يَنْقُصُ مِنْ أَجْرِهِ شَيْءٌ ا هـ هُوَ مَذْهَبُ أَهْلِ السُّنَّةِ وَالْجَمَاعَةِ…
wassalam,

Tabraze Azam

Checked & Approved by Shaykh Faraz Rabbani