俱舍論記 20.49

20.49

「若爾何緣至重說為有」者，說一切有部難。若爾，何緣世尊為此枝髻外道說業過去、盡、滅、變壞而猶是有？既說有言，明過實有。豈彼外道不許過去業曾有性，佛重說有？即由外道信曾有性、不信實有，故佛說有。手執杖行頭上作髻，故名杖髻。盡滅、變壞，過去異名，說業過去、說業盡、說業滅、說業變壞。

Regarding "If so, for what reason [...] repeatedly spoke of it as existent?": This is the Sarvāstivādin objection. If so, for what reason did the World-Honoured One say to the Śikhandin ascetic that karma is past, spent, ceased, and transformed, yet is still existent? Since he used the word "existent," it is clear that the past is real. Could it be that that non-Buddhist did not accept that past karma previously had existence, such that the Buddha had to restate that it is existent? It is precisely because the non-Buddhist believed in its previously having existed, but did not believe in its real existence, that the Buddha spoke of it as existent. He walked holding a staff in hand with a topknot on his head, hence he was called "Staff-Topknot." Spent, ceased, and transformed are alternative names for the past; it means karma is past, karma is spent, karma is ceased, karma is transformed.