...While I am in the world, I am the Light of the world." 6When He had said this, He spat on the ground, and made clay of the spittle, and applied the clay to his eyes, 7and said to him, "Go, wash in the pool of Siloam " (which is translated, Sent). So he went away and washed, and came back seeing... (John 9:6)
The above thing is talking about Prophet Jesus (pbuh) curing the blind (Refer Qur'an 3:49).
Habib, either the son of Fudayk or Furayk's said that his father's eyes became
so white that he had no vision at all. The Messenger of Allah, praise and peace
be upon him, blew some of his saliva in to his eyes whereupon his vision was
immediately restored. He was even seen threading a needle at the age of
Extracted from page 188, section Section 21 – The miraculous healing of the sick and the incurable, from the Book "PROPHET MUHAMMAD - The Cure (Ash-Shifa)" by Judge Eyad. (I actually took it from "Who had the most powerful spit: Jesus or Muhammad?"). There are many other Hadith quoted in that section 21 of that book, talking about the cure/relief by Prophet Muhammad's (pbuh) spit. (Sorry I could not verify them from standard Hadith books).
As others have said and as it is widely believed,
the spit of prophet (pbuh) was considered Barakah
The water left over or the water falling from the wudu of Prophet (pbuh) was considered Barakah.
The prophet (pbuh) touching a person after making some Du'a is considered Barakah.
May the creator guide us all.