It is narrated from the Mother of the Believers, Sayyidah Aishah (may Allah be pleased with her), that she said: The Messenger of Allah (peace and blessings be upon him) said: "Whoever gives a fasting person something to break his fast with will have a reward like his, without anything being reduced from the reward of the (fasting) person; and whatever good deeds he (the fasting person) does, their reward will also go to the one who provided the food, as long as the strength gained from that food remains in him."
No one narrated this hadith from al-Zuhri (may Allah have mercy on him) except al-Hakam bin Abdullah al-Ayli (may Allah have mercy on him), and from al-Hakam only Isa bin Ibrahim (may Allah have mercy on him), while Kathir bin Hisham (may Allah have mercy on him) is alone in narrating it.
Hadith Referenceالمعجم الأوسط / باب الميم / 7136
Hadith Gradingمحدثین:إسناده ضعيف جدًّا، فيه الحكم بن عبد الله الأيلي متروك
Hadith Takhrij«قال الهيثمي: فيه الحكم بن عبد الله الأيلي وهو متروك «مجمع الزوائد ومنبع الفوائد، ج 3، ص 157»» «أخرجه الطبراني فى «الأوسط» برقم: 8438»