What is the earliest written example of Old English?

As mentioned by user067531, The Law Code of Æthelberht of Kent is the earliest known document to have been written in Old English. References to back it up abound.

• "The law-code of the first Christian king of Kent, Æthelberht (died 616), is both the first piece of English law and the earliest datable work composed in English. It survives in a single manuscript as part of a compilation of laws and documents in Latin and Old English made at Rochester five hundred years after Æthelberht’s death, during the episcopate of Bishop Ernulf (reigned 1115–1124)." The British Library
• "The Textus de Ecclesia Roffensi per Ernulphum episcopum (The Book of the Church of Rochester through Bishop Ernulf), usually referred to as the Textus RoffensisOffsite Link, is a collection of documents that includes the tOffsite Link,Law of Aethelberht attributed to Aethelberht of KentOffsite Link, King of Kent from 560 or later to his death of February 24, 616, and the first Anglo-Saxon king to convert to Christianity. This is the first code of English law and the oldest surviving Anglo-Saxon text. It is also the earliest law code of any kind in any Germanic language and the earliest surviving document written in the English language. Though written about 500 years after Aethelberht's code was promulgated, the manuscript predates King John's Magna Carta by almost 100 years." History of Information
• "The Law of Æthelberht is a set of legal provisions written in Old English, probably dating to the early 7th century. It originates in the kingdom of Kent, and is the first Germanic-language law code. It is also thought to be the earliest example of a document written in English, though extant only in an early 12th-century manuscript, Textus Roffensis." Wikipedia

Several short inscriptions on metal or ceramic pots, written in Old English, still survive and some of them seem to predate The Law Code of Æthelberht but, unlike the latter, there is no certainty about dates.

• "The earliest texts in English survive as very short runic inscriptions on metal objects and ceramic pots. The earliest substantial example of English is the lawcode of King Æthelberht of Kent (reigned c. 589–616), but that work survives in just one manuscript (the Textus Roffensis), made in the 1120s. Several Old English manuscripts in the British Library may contain texts that were based on much earlier exemplars and stories, but their dates are uncertain, unlike the lawcode, which can be linked to a particular reign." BL-UK