The evidence is the saying of Allāh, the Exalted:

And (remember) when your Lord proclaimed: "If you are grateful (give thanks), I will give you more (of My blessings), but if you are thankless (ungrateful), My punishment is indeed severe." ^[1]

And He, the Exalted, also said:

Indeed there was for Sabaʾ (Sheba) a sign in their dwelling place, - two gardens on the right hand and on the left (and it was said to them) "Eat of the provision of your Lord, and be grateful to Him, a fair land and an Oft-Forgiving Lord." But they turned away (from the obedience of Allah), so We sent against them a flood released from the dam, and We converted their two gardens into gardens producing bitter bad fruit, and tamarisks, and some few lote-trees. Like this We requited them because they were ungrateful disbelievers. And never do We requit in such a way except those who are ungrateful, (disbelievers).^[2]

Being grateful for the blessings and favours of Allāh leads to an increase in the favours and their persistence. Being ungrateful is a cause of punishment and ending of the blessings and favours as occurred to the people of Sabaʾ. And being grateful is giving obedience to Allāh in what He commanded and refraining from disobedience to Allāh in what He prohibited.

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