Is there a sin upon one who delayed bringing his mother to the hospital, which led to her death after one of the doctors said it would have been possible to save her had she come earlier?

If you did not neglect your mother's treatment, then say: "It is the decree of Allah, and what He wills, He does," and pray for mercy upon her. The statement of the aforementioned doctor holds no value, for lifespans are in the hands of Allah alone. He has decreed and determined them, so they will neither be delayed nor advanced, as stated in His Almighty قول: "And never will Allah delay a soul when its time has come," and His قول: "And when their term comes, they will not remain behind an hour, nor will they precede [it]."