مُسْنَدُ أَحْمَدَ
Musnad Ahmad 3366
Musnad of 'Abdullah bin al-'Abbas bin 'Abdul-Muttalib from the Prophet
It is narrated that Sa'eed bin Jubair said: Ibn 'Abbas (رضي الله عنه) said: The angel brought her (Hajar) to the site of Zamzam, then he struck (the ground) with his heel and the spring started flowing. With human haste she started scooping the water into her waterskin. The Messenger of Allah (ﷺ) said: "May Allah have mercy on the mother of Isma'eel. Had she not been hasty, Zamzam would have been a stream flowing on the surface of the earth."
Musnad Ahmad 3390lts isnad is saheeh, al-Bukhari (3362)]