Musnad Abu Ya'la al-Mawsili 160:132

Wahb ibn Baqiyyah narrated to us, Khalid informed us, from Abd al-Rahman, from al-Ala’, from his father, from Abu Hurayrah, that the Messenger of Allah (may Allah bless him and grant him peace) said: "Whoever sends blessings upon me once, ten good deeds are written for him by it."