Al-Kāfi
Hadith 1621وَ بِإِسْنَادِهِ قَالَ ذُكِرَتْ زَمْزَمُ عِنْدَ أَبِي عَبْدِ اللَّهِ ( عليه السلام ) فَقَالَ أُجْرِيَ إِلَيْهَا عَيْنٌ مِنْ تَحْتِ الْحِجْرِ فَإِذَا غَلَبَ مَاءُ الْعَيْنِ عَذُبَ مَاءُ زَمْزَمَ .
2. Through the same chain of narrators as that of the previous Hadith, the following is narrated: “Once, Zamzam was mentioned before abu ’Abd Allah (a.s.). He (the Imam) said, ’A fountain from under the stone was made to flow on it. When the water of the fountain overwhelms it, water of Zamzam becomes sweet.’”