From good old wikipedia
" Philosophical atheist thought appears in Europe and Asia from the sixth or fifth century BCE."
"n medieval Islam, scholars recognized the idea of atheism, and frequently attacked unbelievers, although they were unable to name any atheists.[26] When individuals were accused of atheism, they were usually viewed as heretics rather than proponents of atheism.[27] One notable figure was the ninth century scholar Ibn al-Rawandi who criticized the notion of religious prophecy including that of Muhammad, and maintained that religious dogmas were not acceptable to reason and must be rejected.[28] Other critics of religion in the Islamic world include the physician and philosopher Abu Bakr al-Razi (865–925), and the poet Al-Ma`arri (973–1057).
In the European Middle Ages, no clear expression of atheism is known. The titular character of the Icelandic saga Hrafnkell, written in the late thirteenth century, says that I think it is folly to have faith in gods. After his temple to Freyr is burnt and he is enslaved, he vows never to perform another sacrifice, a position described in the sagas as goðlauss "godless". Jacob Grimm in his Teutonic Mythology observes that
It is remarkable that Old Norse legend occasionally mentions certain men who, turning away in utter disgust and doubt from the heathen faith, placed their reliance on their own strength and virtue. Thus in the Sôlar lioð 17 we read of Vêbogi and Râdey â sik þau trûðu, "in themselves they trusted",[29]
citing several other examples, including two kings.
In Christian Europe, people were persecuted for heresy, especially in countries where the Inquisition was active. However, Thomas Aquinas' five proofs of God's existence and Anselm's ontological argument implicitly acknowledged the validity of the question about god's existence. The charge of atheism was used as way of attacking one's political or religious enemies. Pope Boniface VIII, because he insisted on the political supremacy of the church, was accused by his enemies after his death of holding (unlikely) atheistic positions such as "neither believing in the immortality nor incorruptibility of the soul, nor in a life to come."[30]"
Of course it is wikipedia as a source, I don't have time right now to check the validity of the sources or the interpretations.
