Septuagint
Early Christian missionaries used the Septuagint in their appeal to the Greek-speaking world and did not hesitate to draw upon documents classified by Jewish rabbinical authorities as uncanonical. The issue of canonicity had not yet become a critical issue when the New Testament literature was being written, and there are numerous references to sources which were not included in the Jewish canon and certain Christian canons. For example, Jude 14-16 quotes the Book of Enoch 1:9, and Hebrews 11:35 f. refers to 2 Maccabees 6-7.10. Christians continued to use the Septuagint, for there was no assertion of a cessation of inspiration among Christians or Jewish Christians, unlike the Talmud (Soṭah 48b) which considers Malachi to be the last prophet of Judaism.
Read more about this topic: Development Of The Old Testament Canon