Soraj Hongladarom said this quote

“ It is recorded in the monastic rules that a monk once performed an abortion on a girl; the Buddha judged his action seriously wrong, which incurred him the highest offense in the monastic rule. A monk committing this kind of wrongful deed must be expelled from the monastic community. The Buddha considered the embryo to be a person like an adult, so the monk who killed the embryo through abortion was judged by Buddhist monastic rules as having committed a crime equal in gravity to killing an adult. In the commentary on the rule stated above, it is stated clearly that killing a human being means destroying human life from the first moment of fertilization to human life outside the womb. So, even though the Buddha himself did not give a clear-cut pronouncement about when personhood occurs, the Buddhist tradition, especially the Theravada tradition, clearly states that personhood starts when the process of fertilization takes place. ”