Musnad Ahmad 32:58

Muhammad ibn Fudayl narrated to us, Yunus ibn ‘Amr—meaning Yunus ibn Abi Ishaq—narrated to us, from Burayd ibn Abi Maryam, from Anas ibn Malik, who said: The Messenger of Allah (ﷺ) said: "Whoever sends one blessing upon me, Allah will send ten blessings upon him, and ten sins will be removed from him."