"Do not murder a child by abortion..." -- the ancient teaching of the Church

"Do not murder a child by abortion or kill a newborn infant." 

Thus says The Didache: The Teaching of the 12 Apostles, which was written down in the 1st century AD, not long after the death and resurrection of Jesus. The Didache (which means, literally "The Teaching") is one of the most ancient early Church documents outside of canon of Sacred Scripture and constitutes the earliest catechism of the Christian Church. In the 4th century AD, St. Athanasius specifically called out this most ancient work as one that should be "read by those who newly join us, and who wish for instruction in the word of godliness."

Here is the above quote placed in greater context:

"And the second commandment of the Teaching is: 

Thou shalt not kill. Thou shalt not commit adultery; thou shalt not corrupt boys; thou shalt not commit fornication. Thou shalt not steal. Thou shalt not use witchcraft; thou shalt not practice sorcery. Thou shalt not procure abortion, nor shalt thou kill the new-born child. Thou shalt not covet thy neighbor's goods. 

Thou shalt not forswear thyself (swear falsely). Thou shalt not bear false witness. Thou shalt not speak evil; thou shalt not bear malice. 

Thou shalt not be double-minded nor double-tongued; for duplicity of tongue is a snare of death. 

Thy speech shall not be false, nor vain, but fulfilled by deed. 

Thou shalt not be covetous, nor rapacious, nor a hypocrite, nor malignant, nor haughty. Thou shalt not take evil counsel against thy neighbor. 

Thou shalt not hate any one, but some thou shalt rebuke and for some thou shalt pray, and some thou shalt love above thine own soul (or, life)."

Read the entire text here: http://www.catholicplanet.com/ebooks/didache.htm