How can one ensure that a mobile phone does not cause brain cancer, and are repeated oaths not to buy it, related to the same subject, considered one oath necessitating a single expiation, or multiple oaths requiring expiations equal to their number?

It has not been proven that mobile phones cause brain cancer. If it were proven by reliable doctors, then it would not be permissible to use it, as it would be throwing oneself into perdition. What is rumored is merely possibilities, and specialists differ on its harms.

Regarding breaking an oath not to buy a mobile phone: - Some jurists hold that atonement is obligatory upon you. - Others hold that if it becomes clear that the mobile phone does not cause harm, then no atonement is due, and this is based on considering the reason for the oath. The first opinion is more cautious.

As for the ruling on multiple atonements for breaking multiple oaths: 1. The majority of scholars hold that repeated oaths concerning a single matter require only one atonement when broken, and they cite the action of Ibn Umar (may Allah be pleased with them both) as evidence. This applies if the oaths are repeated concerning a single matter and the person has not yet broken them. However, if he swore, then broke the oath, then swore again and broke it again, then another atonement becomes obligatory upon him. 2. The Hanafis hold that an atonement is obligatory for each oath. 3. Some Malikis and Shafi'is hold that if the intention was emphasis, then one atonement suffices, but if the intention was to renew the oath, then an atonement is due for each oath. The first opinion is the most preponderant.