Du'a for a mother's protection from sickness

اللَّهُمَّ أَبْعِدْ عَنْهَا الْمَرَضَ، وَارْزُقْهَا طُولَ الْعُمْرِ فِي طَاعَتِكَ

Allahumma ab'id 'anhal-marad, warzuqha tulal-'umri fi ta'atik

O Allah, keep sickness away from her, and grant her a long life in Your obedience.

A general supplication, not a narration from the Prophet (peace be upon him).