A comparable example is the hadith about a sheep that was on the point of death, which a woman slaughtered without its owners’ permission. They asked the Prophet, may Allah bless him and grant him peace, about it, and he permitted them to eat it. He did not require the woman who slaughtered it to compensate them for any reduction in its value caused by slaughtering it, because customary permission existed, and customary permission is equivalent to verbal permission. For this reason:
“The Prophet, may Allah bless him and grant him peace, gave the pledge of allegiance on ‘Uthmān’s behalf in his absence, without asking his permission verbally.”
Likewise, when Abū Talhah invited him and a few others to his home, he set out with everyone in the mosque, knowing that Abū Talhah would gladly welcome them, because of the blessing Allah would bestow. The same applies to the hadith of Jābir. It is also authentically established that a butcher invited him, and he sought his permission for another person accompanying him, because he did not know that the butcher would be as willing to welcome him as he knew Abū Talhah, Jābir and others would be.
Similarly, killing the boy was a case of repelling an aggressor against his parents, because al-Khidr knew that he would tempt them away from their religion. Killing children is permissible if they fight the Muslims; indeed, it is permissible to kill them to repel an attack on property. Thus, it is established in Sahīh al-Bukhārī that when Najdah al-Harūrī asked Ibn ‘Abbās about killing boys, he replied:
“If you know about them what al-Khidr knew about the boy, then kill them; otherwise, do not kill them.”
Likewise, the two Sahīhs relate:
“When ‘Umar asked the Prophet, may Allah bless him and grant him peace, for permission to kill Ibn Sayyād, who was approaching puberty, because he thought him to be the Dajjāl, the Prophet replied, ‘If he is, you will never be given power over him; and if he is not, there is no good for you in killing him.’”
He did not say, “If he is, there is no good for you in killing him.” Rather, he said, “You will never be given power over him.”