The water of ZamZam is for that which it is drunk

A scholar of Ḥadīth writes, ‘I reached the Ḥaram for Ẓuhr Ṣalāh after performing wuḍu. With only five minutes left for Maghib Ṣalāh, I developed an intense urge to attend the call of nature. I thought, ‘If I go back to attend the call of nature, I will not be able to return for Ṣalāh on time. Hence, I feared that my Ṣalāh would become qaḍā, while at the same time the urge to relieve myself was so intense that I feared I may spoil the Ḥaram.

Immediately, the Ḥadīth [ماء زمزم لما شرب له] ‘The water of Zamzam is for that which it is drunk’ came to mind. This prompted me to run to the well of Zamzam and drink a bucket full from it.

He further says that not only did it completely get rid of the urge to attend the call of nature, it also eliminated all the tiredness and weariness that had crept in due to sitting in the Ḥaram and that he performed Fajr Ṣalāh with the same wuḍu!

When Sufyān ibn ‘Uyaynah رحمه الله read this Ḥadīth, a student from his lecture stood up and disappeared from the gathering. Those in the gathering assumed that he had gone to attend the call of nature. After returning a while later, he said, ‘Repeat the Ḥadīth of Zamzam you related earlier.’ His teacher did so. Then the student said, ‘This Ḥadīth is authentic, the chain of narrators are accurate and the promise from Allāh ﷻ of fulfilling the purpose for which it is drunk for is also true. I had gone away to drink some Zamzam water from a bucket and I supplicated to Allāh ﷻ for you (his teacher) to relate to me one hundred Ḥadīth of Ibn Shihāb al-Zuhrī in this gathering.’

Accordingly, his teacher did so. Students would devise various stratagems for the sake of acquiring knowledge.