All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
It is known that Al-Bukhari and Muslim did not aim at gathering the totality of the Saheeh [sound] Ahaadeeth [plural of Hadeeth] of the Prophet ; rather, they were only committed to the rule that the Ahaadeeth which they reported were Saheeh according to the conditions set by each one of them.
Therefore, there is no problem if they had left out so many Saheeh Ahaadeeth which they did not report in their books either for the purpose of being brief (i.e. for fear of excessive length) or for any other purpose.
Indeed, it is confirmed that the Prophet wiped his ears in many narrations in books other than Saheeh Al-Bukhari and Saheeh Muslim.
However, according to our investigation, no interpreter of the Ahaadeeth has mentioned the reason why Al-Bukhari did not mention the narrations implying the permissibility of wiping the ears.
This might be due to them [Al-Bukhari and Muslim] not aiming at gathering the totality of the Saheeh Ahaadeeth. Therefore, there is no reason for asking why Al-Bukhari and Muslim did not mention a given Hadeeth even if it is Saheeh.
Allaah Knows best.