From Sahih Bukhari (Hadith 3369):
Narrated Abu Humaid As-Sa`idi:The people asked, "O Allah's Messenger (ﷺ)! How shall we (ask Allah to) send blessings on you?" Allah's Apostle replied, "Say: O Allah! Send Your Mercy on Muhammad and on his wives and on his offspring, as You sent Your Mercy on Abraham's family; and send Your Blessings on Muhammad and on his offspring, as You sent Your Blessings on Abraham's family, for You are the Most Praiseworthy, the Most Glorious
Reference: Bukhari 3369