Marthad bin Abdullah would never come to the mosque without bringing something to give in charity. One day he came to the mosque carrying onions.I said to him, "Abu al-Khayr, why bring these? They will leave a foul smell on your clothes."He replied, "Nephew, by Allah, there was nothing else in my house that I could give in charity. A man from the companions of the Prophet ﷺ told me that the Prophet ﷺ said, 'The shade of the believer on the Day of Resurrection will be his charity.'"
حدثنا إسماعيل حدثنا محمد بن إسحاق
كان مرثد بن عبد الله لا يجيء إلى المسجد إلا ومعه شيء يتصدق به قال فجاء ذات يوم إلى المسجد ومعه بصل فقلت له أبا الخير ما تريد إلى هذا ينتن عليك ثوبك قال يا ابن أخي إنه والله ما كان في منزلي شيء أتصدق به غيره إنه حدثني رجل من أصحاب النبي ﷺ عن النبي ﷺ قال ظل المؤمن يوم القيامة صدقته
Its chain of transmission is sahih, its narrators are trustworthy and well known. Ibn Khuzayma related the hadith, 4/95, no. 2432, in the book of zakat, and Haythami said, 3/110, "The narrators of Ahmad are trustworthy." Munziri, 2/16, attributed it to Ibn Khuzayma.