With the Samanas

Physically: Siddhartha is much thinner, and hungry as well as thirsty, but he overcomes it and does very well.
Mentally: He is more aware of himself as a person. He can feel pain lesser and at times can go outside of himself, but if only for a few moments.
Spiritually: He is at a high point in his spiritual journey. He feels as if can overcome all. He still feels there is something missing.
Socially: He is still young yet he rises to become a well respected part of the Samana community. He is even able to do what most took years to do.

"Silently Siddhartha stood in the fierce sun's rays, filled with pain and thirst, and stood until he no longer felt pain or thirst."

This sentence from the novel tells us how he became accustomed to pain and suffering. He took in stride however and did what he was told. This all pays off later, though he sees it as usesless at first, when he left the Samanas. This attribute of being able to fast,be patient, and think for himself would ultimately get him to a place many strived for, but could not attain, Nirvana.