It is narrated from Abu Hurairah (may Allah be pleased with him) that he asked: O Messenger of Allah! How should we send blessings upon you in prayer? The Prophet ﷺ replied: "Say: O Allah! Send mercy upon Muhammad ﷺ and upon the family of Muhammad, as You sent mercy upon Ibrahim (peace be upon him), and send blessings upon Muhammad ﷺ and upon the family of Muhammad, as You sent blessings upon Ibrahim (peace be upon him). Then send peace upon me."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 257
Hadith Takhrijاسنادہ ضعیف لشدۃ ضعف شیخ الشافعی، أخرجہ البیہقی فی معرفۃ السنن والآثار: 905۔
It is narrated from Ka'b bin 'Ujrah (may Allah be pleased with him) that the Prophet (ﷺ) used to recite in prayer: "O Allah! Send mercy upon Muhammad (ﷺ) and upon the family of Muhammad, as You sent mercy upon Ibrahim (peace be upon him) and upon the family of Ibrahim, and send blessings upon Muhammad (ﷺ) and upon the family of Muhammad, as You sent blessings upon Ibrahim (peace be upon him) and upon the family of Ibrahim. Surely, You are Praiseworthy and Glorious."
Hadith Referenceمسند الإمام الشافعي / كتاب الصلاة / 258
Hadith Takhrijأخرجہ البخاری، أحادیث الانبیاء، رقم: 3370 - ومسلم، الصلاۃ، باب الصلاۃ علی النبی ﷺ بعد التشہد: 406۔