John was born a stranger to the world of children who used to amuse themselves, as he was serious all the time. Most children took delight in torturing animals whereas, he was merciful to them. He fed the animals from his food until there was nothing left for him, and he just ate fruit or leaves of trees.
John loved reading since childhood. When he grew up, Allah the Exalted called upon him: "0 John! Hold fast to the Scripture (The Torah)." And We gave him wisdom while yet a child. Surah 19: 12
Allah guided him to read the Book of Jurisprudence closely; thus, he became the wisest and most knowledgeable man of that time. Therefore, Allah the Almighty endowed him with the faculties of passing judgments on people's affairs, interpreting the secrets of religion, guiding people to the right path, and warning them against the wrong one.
John reached maturity. His compassion for his parents, as well as for all people and all creatures, increased greatly. He called people to repent their sins.
There are quite a number of traditions told about John. Ibn Asaker related that one time his parents were looking for him and found him at the Jordan River. When they met him, they wept sorely, seeing his great devotion to Allah, Great and Majestic.
Ibn Wahb said that, according to Malik, grass was the food of John Ibn Zechariah, and he wept sorely in fear of Allah.
A chain of narrators reported that Idris Al-Khawlawi said: "Shall I not tell you he who had the best food? It is John Ibn Zechariah, who joined the beasts at dinner, fearing to mix with men."