(319) بَابُ يُؤْجَرُ فِي كُلِّ شَيْءٍ حَتَّى اللُّقْمَةُ يَرْفَعُهَا إِلَى فِي امْرَأَتِهِ
Sa'd ibn Abi Waqqas transmitted that the Prophet, may Allah blesshim and grant him peace, said to him, "You do not spend anything by whichyou desire the face of Allah Almighty but that you art rewarded for it,even what you place in your wife's mouth."
Reference: Al-Adab Al-Mufrad 752
In-book reference: Book 32, Hadith 7
English translation: Book 32, Hadith 752