Du'a for a mother's devotion

اللَّهُمَّ اجْعَلْهَا مِنَ الذَّاكِرِينَ لَكَ وَالشَّاكِرِينَ لَكَ

Allahumma-j'alha min adh-dhakirina laka wash-shakirina lak

O Allah, make her among those who remember You and are thankful to You.

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