وعن جُندب بن عبد الله رضي الله عنه
قال: قال رسول الله صلى الله عليه وسلم: «قال رجل: والله لا يغفر الله لفلان، فقال الله عز وجل: من ذا الذي يتألى علي أن لا أغفر لفلان! فإني قد غفرت له، وأحبطت عملك»
The Messenger of Allah (sallallahu alayhi wa sallam) said, “Once someone said: ‘By Allah! Allah will not forgive such and such (a person).’ Thereupon Allah, the Exalted and the Glorious, said: ‘Who is he who takes an oath in My Name that I will not grant pardon to so-and-so? I have granted pardon to so-and-so and rendered your good deeds fruitless.’”.
Riyad as-Salihin 1576, Book 18, The Book of the Prohibited actions, Hadith 66. 1 min read