In 30 years I have never found an ancient Buddhist Sutra quoting the Buddha saying there was no God, in fact many have him interactive with the God's of India. But without a doubt he taught non attachment. How much evil has been done in the name of this or that person's idea of God. Clearly if he taught on God it was to abandon one's idea of God. Let God be God, give God no name, no culture, no nationality. Lose your attachment to what you would have God be. Once you think you know God you then resent others with a different idea of God. You soon think you even know the mind of God. Only Evil seems to follow.
The Buddha's teachings in both Mahayana and Theravada Buddhism are for all intents and purpose essentially atheistic, although neither deny the existence of beings that might be called "gods." In point of fact the Buddha himself rejected metaphysical speculation as a matter of principle, and his teachings focused entirely on the practical ways to end suffering. Many people have interpreted his teaching on non-attachment as atheism. And many have ignored Buddha's first sermon where he plainly says his teaching's purpose is to mitigate the heritage of human sorrow. They have chosen to believe he was teaching a path to something they called "enlightenment" in English. How much suffering has been both endured and inflicted in the name of this so called enlightenment no man can tell.
On the other hand, the Buddha did not explicitly rule out the existence of a God or gods. As Buddhism filtered through many cultures and countries it picked up many hitchhikers. In both Mahayana and Theravada Buddhism the local God's and spirits attached themselves to Buddha. The Hindu god's and deities traveled along for the ride. In Burma the "Nat" hitched a ride. Among the most popular Buddhist deities in the east are Kuan Yin, the Medicine Buddha, the Laughing Buddha and the Green and White Taras. As local Buddhist wrote their own sutra's classifications arose for the various Avatars of Buddhist Ideals. there are Buddha's Gautama Buddha (Shakyamuni) Laughing Buddha/Future Buddha (Maitreya) Medicine Buddha/Healing Buddha Five Dhyani Buddhas Dipamkara (Kasyapa) Buddha. The newer Mahayana Buddhist added the Bodhisattvas Five Bodhisattvas of Compassion Tara Kuan Yin etc. In Theravada Buddhism you have yourArhats which spread to Mahayana , at least 16 Sravakas (Tibetan) 18 Lohans (Chinese) . In China just a few of the Chinese Buddhist Deities are Kuan-Yin Jade Maiden Golden Youth Kuan-Ti (Sangharama) Wei-To (Skanda) Four Guardian Kings (Si-Ta-Tien-Wang) . In Tibet the Tibetan Wrathful Deities Yama Mahakala Yamantaka Kubera Hayagriva Palden Lhamo Tshangs pa Begtse Nagas Lha-mo all jumped aboard for the ride.
Since this blog is about Zen, the Japanese form of Chan we can't leave out their extensive hierarchy of hangers on. Leading the list of course are the Buddhas, followed in order by the numerous Bodhisattvas, the Wisdom Kings, the Deities, the "Circumstancial appearances" and lastly the patriarchs and eminent religious people Ad infinitum.
The actual existence of any of these Spirits, Deities, Gods and Avatars is something I will leave to the reader to decide. I would note that they are often useful tools to mentally crystalize an idea or concept in the teachings. Like the parable of the raft, they are probably best left on the bank once the river is crossed.