Allama Manawi writes in his commentary: This is an exaggeration of the intensity of their closeness and relationship with each other

Dailami, Firduas Al-Akhbar, V.3, page 89; Manawi, Faiz al-Qadir, V.4, page 471; Ibn Hajar al-Asqalani, Zahr al-Firdaus, V.2, page 316 as a statement; Kharazmi in Al-Manaqib (page 144) and Ibn Maghazli in Manaqib (page 98) have narrated that the Messenger of Allah (s.a.w.a.) said, “Ali’s relation to me is like the relation of a head to the body.” Also, they narrate through another chain of transmission from the Messenger of Allah (s.a.w.a.) as saying, “Ali’s relation to me is like that of my head to my body.”

Also, refer to Suyuti, Al-Jami' as-Saghir, V.2, page 177; Muttaki Hindi, Kanz al-Ummal, V. 11, page 603.