Why is it considered "borrowing" when they believe some idea to be true? Even if its an ancient Hindu concept of a singular God, it is all the same. I think its a very childish thing to suggest its a different "God".
Whether you believe in any of the Prophets, Jewish, or Muslim or otherwise, none of that is material to this concept. The idea is about "belief in one entity" that is the creator. Humans tend to over
complicate it.
For further reading:
The words Allah and Khuda in the SGGS
The word ਖਦਾਇ has been used 34 times, while the word ਖਦਾਈ has been used 8 times in the
Guru Granth Sahib.
The word Allah is used by the following authors in the following lines:
Guru Nanak Dev
ਬਾਬਾ ਅਲਹ ਅਗਮ ਅਪਾਰ ॥
O Baba, the Lord Allah is Inaccessible and Infinite.
ਅਲਾਹ ਅਲਖ ਅਗੰਮ ਕਾਦਰ ਕਰਣਹਾਰ ਕਰੀਮ ॥
He is Allah, the Unknowable, the Inaccessible, All-powerful and Merciful Creator.
ਕਲਿ ਮਹਿ ਬੇਦ ਅਥਰਬਣ ਹੂਆ ਨਾਉ ਖਦਾਈ ਅਲਹ ਭਇਆ ॥
In the Dark Age of Kali Yuga, the Atharva Veda became prominent; Allah became the Name of God.
ਆਦਿ ਪਰਖ ਕਉ ਅਲਹ ਕਹੀਝ ਸੇਖਾਂ ਆਈ ਵਾਰੀ ॥
The Primal Lord God is called Allah. The Shaykh's turn has now come.
Namdev
ਛੋਡਿ ਰਾਮ ਕੀ ਨ ਭਜਹਿ ਖਦਾਇ ॥੬॥
and she said, "Why don't you abandon your Lord Raam, and worship his Lord Allah?"||6||
Fareed
ਭਿਜਉ ਸਿਜਉ ਕੰਬਲੀ ਅਲਹ ਵਰਸਉ ਮੇਹ ॥
My blanket is soaked, drenched with the downpour of the Lord's Rain. ਪੰਨਾ 1379, ਸਤਰ 4
Guru Arjun Dev
ਝਕੋ ਅਲਹ ਪਾਰਬਰਹਮ ॥੫॥੩੪॥੪੫॥
The Muslim God Allah and the Hindu God Paarbrahm are one and the same. ||5||34||45||
ਅਲਹ ਅਗਮ ਖਦਾਈ ਬੰਦੇ ॥
O slave of the inaccessible Lord God Allah,
ਹੂਰ ਨੂਰ ਮਸਕ ਖਦਾਇਆ ਬੰਦਗੀ ਅਲਹ ਆਲਾ ਹਜਰਾ ॥੫॥
God is the beauty, the light and the fragrance. Meditation on Allah is the secluded meditation chamber. ||5||
ਝਕ ਗਸਾਈ ਅਲਹ ਮੇਰਾ ॥
The One Lord, the Lord of the World, is my God Allah.
ਅਲਹ ਰਾਮ ਕੇ ਪਿੰਡ ਪਰਾਨ ॥੪॥
My body and breath of life belong to Allah - to Raam - the God of both. ||4||
Kabeer
ਰੋਜਾ ਧਰੈ ਮਨਾਵੈ ਅਲਹ ਸਆਦਤਿ ਜੀਅ ਸੰਘਾਰੈ ॥
You keep your fasts to please Allah, while you murder other beings for pleasure.
ਸਾਚ ਕਤੇਬ ਬਖਾਨੈ ਅਲਹ ਨਾਰਿ ਪਰਖ ਨਹੀ ਕੋਈ ॥
Your holy scriptures say that Allah is True, and that he is neither male nor female.
ਅਲਹ ਗੈਬ ਸਗਲ ਘਟ ਭੀਤਰਿ ਹਿਰਦੈ ਲੇਹ ਬਿਚਾਰੀ ॥
Allah is hidden in every heart; reflect upon this in your mind.
ਅਲਹ ਝਕ ਮਸੀਤਿ ਬਸਤ ਹੈ ਅਵਰ ਮਲਖ ਕਿਸ ਕੇਰਾ ॥
If the Lord Allah lives only in the mosque, then to whom does the rest of the world belong?
ਅਲਹ ਰਾਮ ਜੀਵਉ ਤੇਰੇ ਨਾਈ ॥
O Allah, O Raam, I live by Your Name.
ਕਬੀਰ ਪੂੰਗਰਾ ਰਾਮ ਅਲਹ ਕਾ ਸਭ ਗਰ ਪੀਰ ਹਮਾਰੇ ॥੫॥
Kabeer is the child of God, Allah, Raam. All the Gurus and prophets are mine. ||5||
ਅਵਲਿ ਅਲਹ ਨੂਰ ਉਪਾਇਆ ਕਦਰਤਿ ਕੇ ਸਭ ਬੰਦੇ ॥
First, Allah created the Light; then, by His Creative Power, He made all mortal beings.
ਅਲਹ ਅਲਖ ਨ ਜਾਈ ਲਖਿਆ ਗਰਿ ਗੜ ਦੀਨਾ ਮੀਠਾ ॥
The Lord Allah is Unseen; He cannot be seen. The Guru has blessed me with this sweet molasses.
ਕਬੀਰ ਅਲਹ ਕੀ ਕਰਿ ਬੰਦਗੀ ਜਿਹ ਸਿਮਰਤ ਦਖ ਜਾਇ ॥
Kabeer, worship the Lord Allah; meditating in remembrance on Him, troubles and pains depart.
But apart from that, one has to know a bit about Sufism as well as Sikhism to understand the link between the two. Guru Nanak was actually equally critical of Islam and Hinduism as well as fond of certain ideas within them. That tells me that he studied them both and I find it hard to believe it all ended at the concept of the one God.