How can one reconcile the two hadiths: "Every son of Adam errs, and the best of those who err are those who repent," and "There is no one among the children of Adam who has not erred, or intended to err, except for Yahya ibn Zakariyya (John the son of Zechariah)"?

Summary of the answer: The hadith "Every son of Adam errs, and the best of those who err are those who repent" has a weak chain of narration (sanad), as it was narrated singularly by Ali ibn Mas'adah al-Bahili, who is disputed among scholars, and some scholars have deemed him weak.

As for the hadith of Ibn Abbas, "There is no one among the children of Adam but has erred, or intended to err, except Yahya ibn Zakariyya," it is also weak due to Ali ibn Zayd ibn Jud'an, but some scholars have authenticated it due to supporting narrations (shawahid).

There is no contradiction between the two hadiths according to those who consider both hadiths weak. However, according to those who consider them authentic, the hadith "Every son of Adam errs" is a general statement intended for the majority, and Yahya ibn Zakariyya is exempted from it, as he was infallible from sin.

Specificity applies to narrative texts just as it applies to commands, like the Almighty's saying: "destroying everything by the command of its Lord," which was specified to destroy certain things, not absolutely everything.