Saad bin Abu Waqqas reported that the Messenger of Allah ﷺ said, "You will never spend anything seeking the pleasure of Allah without being rewarded for it, even what you place in your wife's mouth."
أنه أخبره أن رسول الله ﷺ قال: إنك لن تنفق نفقة تبتغي بها وجه الله إلا أجرت عليها حتى ما تجعل في فم امرأتك.
Bukhari narrated it in the Book of Faith (56), and Muslim in the Book of Bequests (1628), both from the hadith of Zuhri, who said, Amir bin Saad bin Abu Waqqas told me, from his father, and he related it, and the wording given is Bukhari's. In a wording of Muslim's, "even the morsel you place in your wife's mouth." Both of them have it within a longer context, which is mentioned in its proper place.