If I am not wrong, earliest use of the English phrase “early Buddhism” to refer to both Pali and Chinese early Buddhist texts is:
Choong Mun-keat. The Notion of Emptiness in Early Buddhism (1995; second revised edition, Motilal Banarsidass, Delhi, 1999).
“Within Buddhist studies it is widely assumed that only the Pāli texts represent “early Buddhism”. Naturally, the Pāli texts are important sources for the study of early Buddhism; however, the Pāli canon, as the scripture of the southern Buddhist tradition (the self-styled “Theravāda”, Teaching of the Elders), belonging to the school Tāmraśāṭīya (or Tāmraparṇīya, the Buddhist sect or monks of Tāmraparṇī), represents only one of the various “early Buddhist schools” (so-called “Hīnayāna Buddhism”). If one only considers and emphasises Pāli sources, without comparing them with the Chinese versions, then one is studying Pāli Buddhism, not early Buddhism. For the study of early Buddhism it is essential to pay attention to both the Pāli and the Chinese versions of the early canon . Therefore, in this book, the references to emptiness in early Buddhism cover not only the Pāli texts, but also the Chinese versions representing other early Buddhist schools.” (pp. viii-ix)
Pages viii-ix from Notion of Emptiness in Early Buddhism Choong Mun-keat.pdf (928.3 KB)