The Sarvāstivādins acknowledged that their canoncial Abhidharma texts were composed by disciples but still generally considered them to be the word of the Buddha (buddhavacana). Saṃghabhadra's Abhidharmanyāyānusāra:
As the abhidharma [texts] were compiled by the great disciples on the basis of the Buddha's teaching, they are approved by the Buddha; they are also buddha-vacana. As they are in accord with the knowledge which knows fully the causes and effects of defilement and purification, they are like the sūtra-s. If what has been approved by the Buddha is not called buddha-vacana, then innumerable sūtra-s would have to be abandoned!
That is, all of the suttas spoken by Sāriputta, etc., would also have to be dismissed if one is going to dismiss everything that wasn't spoken directly by the Buddha.
It was the Dārṣṭāntika and Sautrāntika authors who didn't accept the Abhidharma as the word of the Buddha, although they often still used similar abhidharma concepts and categories. It seems that the earliest extant text that refers to Sautrāntika ideas and interpretations by name is Vasubandhu's auto-commentary on his Abhidharmakośa called the Abhidharmakośabhāsya. However, these Sautrāntika ideas likely predate Vasubandhu's auto-commentary.