The Codex Sinaiticus, designated by siglum א‎ [Aleph] or 01, δ 2, also called Sinai Bible, is a fourth-century Christian manuscript of a Greek Bible, containing the majority of the Greek Old Testament, including the deuterocanonical books, and the Greek New Testament, with both the Epistle of Barnabas and the Shepherd of Hermas included. It is written in uncial letters on parchment. It is one of the four great uncial codices. Along with Codex Alexandrinus and Codex Vaticanus, it is one of the earliest and most complete manuscripts of the Bible, and contains the oldest complete copy of the New Testament. It is a historical treasure, and using the study of comparative writing styles (palaeography), it has been dated to the mid-fourth century.

The Epistle of Barnabas is a Greek epistle written between AD 70 and 132. The complete text is preserved in the 4th-century Codex Sinaiticus, where it appears at the end of the New Testament, following the Book of Revelation and before the Shepherd of Hermas. For several centuries it was one of the "antilegomena" ("disputed") writings that some Christians looked on as sacred scripture, while others excluded them. Eusebius of Caesarea classified it with excluded texts. It is mentioned in a perhaps third-century list in the sixth-century Codex Claromontanus and in the later Stichometry of Nicephorus appended to the ninth-century Chronography of Nikephoros I of Constantinople. Some early Fathers of the Church ascribed it to the Barnabas who is mentioned in the Acts of the Apostles, but it is now generally attributed to an otherwise unknown early Christian teacher, although some scholars do defend the traditional attribution. It is distinct from the Gospel of Barnabas.