With Ambaṭṭha 1.20.8

1.20.8

“taṃ kiṃ maññasi, ambaṭṭha, kinti te sutaṃ brāhmaṇānaṃ vuddhānaṃ mahallakānaṃ ācariyapācariyānaṃ bhāsamānānaṃ kutopabhutikā kaṇhāyanā, ko ca kaṇhāyanānaṃ pubbapuriso”ti?

Then the Blessed One said to Ambaṭṭha the Brahman: ‘Then this further question arises, Ambaṭṭha, a very reasonable one which, even though unwillingly, you should answer. If you do not give a clear reply, or go off upon another issue, or remain silent, or go away, then your head will split in pieces on the spot. What have you heard, when Brahman old and well stricken in years, teachers of yours or their teachers, were talking together, as to whence the Kaṇhāyanas draw their origin, and who the ancestor was to whom they trace themselves back?’
And when he had thus spoken Ambaṭṭha remained silent. And the Blessed One asked the same question again. And still Ambaṭṭha remained silent. Then the Blessed One said to him: ‘You had better answer, now, Ambaṭṭha. This is no time for you to hold your peace. For whosoever, Ambaṭṭha, does not, even up to the third time of asking, answer a reasonable question put by a Tathāgata (by one who has won the truth), his head splits into pieces ‘on the spot.’