Paradise is at her feet
فَالْزَمْهَا فَإِنَّ الْجَنَّةَ تَحْتَ رِجْلَيْهَا
Falzamha, fa-inna-l-jannata tahta rijlayha.
"Then stay with her, for Paradise is beneath her feet."
Narrated by Mu'awiyah ibn Jahimah as-Sulami. Sunan an-Nasa'i 3104 (hasan sahih)
A short reflection
Jahimah came wanting to go out and fight, and the Prophet ﷺ asked whether he had a mother, then sent him back to her. The popular wording "Paradise is under the feet of mothers" has no sound chain of its own; this is the authentic narration behind it.