From Sahih Bukhari (Hadith 5735):
Narrated `Aisha:During the Prophet's fatal illness, he used to recite the Mu'auwidhat (Surat An-Nas and Surat Al- Falaq) and then blow his breath over his body. When his illness was aggravated, I used to recite those two Suras and blow my breath over him and make him rub his body with his own hand for its blessings." (Ma`mar asked Az-Zuhri: How did the Prophet (ﷺ) use to blow? Az-Zuhri said: He used to blow on his hands and then passed them over his face
Reference: Bukhari 5735