Irenaeus of Lyon included a version of the "rule of faith" in his late 2nd century summary of the Christian faith, On the Apostolic Preaching, I.1.6. Here it is; I added the text in brackets and removed a few phrases that Irenaeus used to introduce each 'article' so that, in the form below, it reads more like the classical creeds.
[We believe in] God, the Father, uncreated, uncontainable, invisible, one God, the Creator of all.
[We believe in] the Word of God, the Son of God, Christ Jesus our Lord, who was revealed by the prophets according to the character of their prophecy and according to the nature of the economies of the Father, by whom all things were made, and who, in the last times, to recapitulate all things, became a man amongst men, visible and palpable, in order to abolish death, to demonstrate life, and to effect communion between God and man.
[We believe in] the Holy Spirit through whom the prophets prophesied and the patriarchs learnt the things of God and the righteous were led in the path of righteousness, and who, in the last times, was poured out in a new fashion upon the human race renewing man, throughout the world, to God.
This is remarkable for a number of reasons. Here are a few:
1. Irenaeus has a lot more to say about the Holy Spirit than either the Nicene (with the additions from 381) or the Apostles' Creed. The way a lot of people talk about the historical development of doctrine you would think no one had an articulate and distinct understanding of the Holy Spirit until the late 4th century, but this was written about two hundred years before that.
2. The major creeds make very few references to the Hebrew Scriptures. Irenaeus, on the other hand, is all about articulating how the Word and the Spirit relate to 'the prophets' (who revealed the Word and spoke through the Spirit), but he also mentions the patriarchs (who were taught by the Spirit). The fact that he goes out of his way to describe the Christian faith in terms of its relationship to the Old Testament is significant. The God-Man Jesus Christ stands in continuity with the God of the prophets; this is a crucial point for Irenaeus as it was, for instance, in the great speeches of Acts of the Apostles.
3. There's no explicit Virgin Birth. Irenaeus elsewhere talks about the Virgin Birth of Jesus, so his failure to mention it here isn't because he didn't believe it or think it was important: according to Irenaeus, Mary the obedient virgin recapitulates Eve the disobedient virgin, in a similar fashion to Christ's recapitulation of Adam. But it is interesting that it doesn't make it into his creed - instead he focusses on his understanding of incarnation, recapitulation and communion between humanity and God.
4. Christ didn't just defeat death; he demonstrated life. I love that phrase. Is this a reference to his teachings, miracles, etc.? The major creeds are silent on these things, and there is at least a chance that they might be part of what is intended here. But the main thing this phrase drives at is the bigger picture: that Christ puts on display what a real, fully actualized human life looks like. He recapitulates, or 're-heads' humanity, being the Adam that Adam could never have been. Or, as one of the teenagers at my church likes to say, Christ was "Adam 2.0".
5. There are several different articulations of the shape of salvation and one mention of righteousness, but no talk of sin. The cross is given a gloss from the point of view of the resurrection as having abolished death, but there is no mention of sin or the forgiveness of sins. The classical creeds mention the forgiveness of sins and the resurrection of the dead. Irenaeus is singularly occupied with an account of the latter, and he does more than just mention it - he fleshes it out.
6. Irenaeus' creed leads to a form of oneness with God. The Word effects communion between humanity and God, and the Spirit renews humanity to God. This creed is much more specific about the actual shape of the gospel than the classical creeds.