God is ONE

Deuteronomy 6:4

"Hear, O Israel! The LORD is our God, the LORD is one!

The literal word meanings are roughly as follows:

Sh'ma — listen, or hear and do (according to the Targum, accept)

Yisrael — Israel, in the sense of the people or congregation of Israel

Adonai — often translated as "LORD", it is read in place of the YHWH written in the Hebrew text; Samaritans say Shema, which is Aramaic for "the [Divine] Name" and is the exact equivalent of the Hebrew "ha-Shem", which Rabbinic Jews substitute for "Adonai" in a non-liturgical context such as everyday speech.

Eloheinu — the plural 1st person possessive of אֱלֹהִים‎ Elohim, meaning “our God”.

Echad — the unified and cardinal number one אֶחָד‎

This first verse of the Shema relates to the kingship of God. The first verse, "Hear, O Israel: the LORD our God is one LORD," has ever been regarded as the confession of belief in the One God. Due to the ambiguities of the Hebrew language, there are multiple ways of translating the Shema:

"Hear, O Israel! Adonai is our God! Adonai is One!" and,

"Hear, O Israel! Adonai is our God – Adonai alone."

Mark 12:29

Jesus replied, “This is the most important: ‘Hear O Israel, the Lord our God is One Lord, 

In Islam

The words used in the Shema prayer are similar to the words of Sura 112 (Al-Tawhid or Monotheism) in Quran. The words "أَحَدٌ" in Arabic is identical to the word "אֶחָד" in Hebrew.
Arabic: قُلْ هُوَ اللَّهُ أَحَدٌ‎‎ - Qul Huwa 'Llāhu ʾAḥad ("Say, He is Allah the One")
Hebrew: :שְׁמַע יִשְׂרָאֵל יהוה אֱלֹהֵינוּ יהוה אֶחָד‎ - Sh'ma Yisra'el YHWH Eloheinu YHWH Eḥad

Ahad/أَحَدٌ = Echad/Achd/Ekhad/אֶחָד

                                                                                                                 

In the name of God, the Gracious, the Merciful.

Say, “He is God, the One (أَحَدٌ).

God, the Absolute.

He begets not, nor was He begotten.

And there is nothing comparable to Him.

(QURAN 112 (1 - 4)Monotheism /al-Ikhlas )  

Isaiah 46:9

"Remember the former things long past, For I am God, and there is no other; I am God,and there is no one like Me,"

Your God is one God. There is no god but He, the Benevolent, the Compassionate.

(QURAN (2:163)  The Heifer/ al-Baqarah)

Joel 2:27 

"Thus you will know that I am in the midst of Israel, And that I am the LORD your God, And there is no other; And My people will never be put to shame.

Isaiah 43:12

"It is I who have declared and saved and proclaimed, And there was no strange god among you; So you are My witnesses," declares the LORD,"And I am God. 

1 Corinthians 8:4

So about eating food sacrificed to idols: We know that an idol is nothing at all in the world, and that there is no God but one. 

Isaiah 42:8 

I am the LORD; that is my name! I will not give my glory to anyone else, nor share my praise with carved idols.

Isaiah 44:6 

Thus says the Lord, the King of Israel and his Redeemer, the Lord of hosts: “I am the first and I am the last; besides me there is no god.”

 Deuteronomy 4:35 

To you it was shown, that you might know that the LORD is God; there is no other besides him.

1 Corinthians 8:5-6 

For although there may be so-called gods in heaven or on earth—as indeed there are many “gods” and many “lords”— yet for us there is one God, the Father, from whom are all things and for whom we exist, and one Lord, Jesus Christ, through whom are all things and through whom we exist.

Note: One means single and alone without partner

The Divine Book (pt.1/10)

Source: 
http://www.clearquran.com
http://biblehub.com

Hindu Scriptures

"Those whose intelligence has been stolen by material desires surrender unto demigods and follow the particular rules and regulations of worship according to their own natures."
                   [Bhagavad Gita 7:20]

"Ekam evadvitiyam"
"He is One only without a second."
        [Chandogya Upanishad 6:2:1]1

"Na casya kascij janita na cadhipah."
"Of Him there are neither parents nor lord."
         [Svetasvatara Upanishad 6:9]2

"Na tasya pratima asti"
"There is no likeness of Him."
        [Svetasvatara Upanishad 4:19]3

The oldest of all the vedas is Rigveda. It is also the one considered most sacred by the Hindus. The Rigveda states in Book 1, hymn 164 and verse 46:
"Sages (learned Priests) call one God by many names."
                          [Rigveda 1:164:46]