Rigveda 1.164.46

इन्द्रं मित्रं वरुणमग्निमाहुरथो दिव्यः स सुपर्णो गरुत्मान् ।
एकं सद्विप्रा बहुधा वदन्त्यग्निं यमं मातरिश्वानमाहुः ॥

Indram mitram varunamagnimahuratho divyah sa suparno garutman,
Ekam sad vipra bahudha vadantyagnim yamam matarisvanamahuh. 

Meaning of the mantra.

1. Truth is one, seekers call it by various names.

2. It is clearly stated in this Mantra that though the Supreme Being—God is One, He is called by various names such as Indra, Mitra, Varuna, Agni, Yama, Matarishva etc. to denote His different attributes.

3. Ekam Sat Vipra Bahudha Vadanti – Satya or truth is one, rishis or sages call it by various ways or names.

Truth is one, seekers call it by various names.