Al-Imām al-Qurtubī in his tafsīr of the verse:

إن الله وملائكته يصلون على النبي يا أيها الذين آمنوا صلوا عليه وسلموا تسليما

"Verily, Allah and His angels bless the Prophet. O you who believe, ask (Allah) to bless him and grant him abundant peace." (33:56)

reported from ‘Umar bin al-Khattāb that the Prophet said:

من صلى علي وسلم علي في كتاب لم تزل الملائكة يصلون عليه ما دام اسمي في ذلك الكتاب

He who sends prayers and peace on me in a book, the angels never cease in sending prayers upon him as long as my name is in that book

[Imām al-Qurtubī in his tafsīr, Jāmī'.]