Richard Gombrich (2006). Theravada Buddhism. Routledge. p. 47. ISBN978-1-134-90352-8., Quote: "All phenomenal existence [in Buddhism] is said to have three interlocking characteristics: impermanence, suffering and lack of soul or essence."
[a] Christmas Humphreys (2012). Exploring Buddhism. Routledge. pp. 42-43. ISBN978-1-136-22877-3.
[b] Brian Morris (2006). Religion and Anthropology: A Critical Introduction. Cambridge University Press. p. 51. ISBN978-0-521-85241-8., Quote: "(...) anatta is the doctrine of non-self, and is an extreme empiricist doctrine that holds that the notion of an unchanging permanent self is a fiction and has no reality. According to Buddhist doctrine, the individual person consists of five skandhas or heaps - the body, feelings, perceptions, impulses and consciousness. The belief in a self or soul, over these five skandhas, is illusory and the cause of suffering."
[c] Richard Gombrich (2006). Theravada Buddhism. Routledge. p. 47. ISBN978-1-134-90352-8., Quote: "(...) Buddha's teaching that beings have no soul, no abiding essence. This 'no-soul doctrine' (anatta-vada) he expounded in his second sermon."