Allah mentions thankfulness even before belief in Him

يَا أَيُّهَا الَّذِينَ آمَنُوا كُلُوا مِن طَيِّبَاتِ مَا رَزَقْنَاكُمْ وَاشْكُرُوا لِلَّهِ إِن كُنتُمْ إِيَّاهُ تَعْبُدُونَ
O you who believe! Eat of the good things We have provided for you, and give thanks to Allah, if it is Him that you serve. The Quran 2:172

ARE YOU GRATEFUL?
There is something in our life that we did not earn and do not own, yet it is given to us all the time.
This thing is this moment, and the next moment and all of the moments of our existence. There are no good reasons to show that we own these moments of our existence. We did not create the world and the life that it contains — including our own. Also, there are no good reasons to show that we have earned these moments, or that we deserve another moment in our life. Such a blessing can never be acquired or repaid by someone who doesn’t even have the power to create a single fly, and is a being that is dependent and needy.

Therefore, if someone has given us something that we haven’t earned and something that we don’t own, then that should instil an immense sense of gratitude in our heart.

Who should we be grateful to? That’s simple. The One who created life and gave it to us — Allah.

Gratitude in Islam is a form of worship. So do not be like the one who was given 100 rands a day, and after a year he started thanking the R100 and not the One who gave it to him. Being ungrateful to Allah is irrational as well as a form of spiritual and intellectual malaise.

Allah reminds us,

إِنَّ ٱللَّهَ لَذُو فَضْلٍ عَلَى ٱلنَّاسِ وَلَـٰكِنَّ أَكْثَرَهُمْ لَا يَشْكُرُون
Truly, Allah is full of Bounty to mankind, but most of them are ungrateful. The Qur’an 10:60

وَٱشْكُرُوا۟ نِعْمَتَ ٱللَّهِ إِن كُنتُمْ إِيَّاهُ تَعْبُدُونَ
And be grateful for the Graces of Allah, if it is He Whom you worship. The Qur’an 16:114

The Concept of Thankfulness in Islam
According to Islam, one of our foremost duties is to be grateful to Allah for all of His blessings. We can describe three levels of thankfulness:

1. To realize and appreciate all blessings by and within the heart.
2. To say thanks with the tongue.
3. To express gratitude by doing righteous deeds.

In other words, the first level is the appreciativeness and gratefulness that we feel in our hearts. Then we fortify that thankfulness through our speech. And the third level is when we prove by our deeds that we are truly thankful to Allah.