Sa'd bin Abu Waqqas (May Allah be pleased with him) reported in a Hadith included in the chapter of Intention, that Messenger of Allah (ﷺ) said, "Whatever you spend seeking thereby the Pleasure of Allah, will have its reward, even the morsel which you put in the mouth of your wife".[Al-Bukhari and Muslim].
Arabic/English book reference: Book 1, Hadith 292