Musnad Ahmed: Hadith 2278

Ibraheem brought Isma'eel and Hajar, and left them in Makkah at the site of Zamzam…. and he narrated the hadeeth. Then she came from al-Marwah to Isma’eel, and the spring had begun to flow. She started digging with her hands around the spring, to make a hole so that the water would gather in this hole, then she took her jug and scooped up some water into her waterskin. The Messenger of Allah (ﷺ) said: “May Allah have mercy on her; if she had left it alone it would have been a spring flowing (on the surface) until the Day of Resurrection.”