Proof of “Idol” Worship in the Vedic literature

First off, “idol worship” is a wrong term – Hindus don’t worship idols. Any stone or animal is not God, so we don’t pray to random objects in the street. Rather we worship the Deity who presence is invocated in a material object according to Vedic rituals. The correct term is mūrti-pūja whose approximate translation is “Deity worship” or “icon worship”.

Inspired by this Hinduism.SE answer, I collected the original verses here.

Ṡukla-Yajur-Veda

या ते॑ अग्ने यःश॒या त॒नूर्वर्षि॑ष्ठा गह्वरे॒ष्ठा ।
उ॒ग्रं वचो॒ अपा॑वधीत्त्वे॒षं वचो॒ अपा॑वधी॒त्स्वाहा॑ ।
या ते॑ अग्ने रजःश॒या त॒नूर्वर्षि॑ष्ठा गह्वरे॒ष्ठा ।
उ॒ग्रं वचो॒ अपा॑वधीत्त्वे॒षं वचो॒ अपा॑वधी॒त्स्वाहा॑ ।
या ते॑ अग्ने हरिश॒या त॒नूर्वर्षि॑ष्ठा गह्वरे॒ष्ठा ।
उ॒ग्रं वचो॒ अपा॑वधीत्त्वे॒षं वचो॒ अपा॑वधी॒त्स्वाहा॑ ।। 5/8 ।।