Assalaam u alaikum warehmatullahi wabarakaatuhu.. I have a query ..actually I want to know what should a person do if any unknown person refilled his mobile say by any amount by his mistake in typing the mobile no. What should a person do in that case if the persons identity is not revealed?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.

If someone you do not know recharged your mobile account balance by mistake, you have to return this amount to him if possible. There is no need to know the identity of the sender; you just need to know his mobile number. If you are not able to know the number and it is possible to contact the company and ask for help to identify from which number the transaction was made, then you are obliged to do so. However, if there is no way to identify that person, you can offer the amount in charity and dedicate the reward to that person or you may use it for your personal benefit.

Shaykh Al-Islam Ibn Taymiyyah wrote about disposal of the property whose owner is unknown (and unidentifiable): "It is incumbent on the person who found a lost item to return it to its rightful owner; if he is unable to return it to him, then what is unknown is like what is non-existent. This is evidenced by the Hadeeth on the Luqatah (lost and found property) as the Prophet, sallallaahu ‘alayhi wa sallam, said: 'Whoever finds lost property, let him ask one or two men of good character to be witnesses to that, then he should not alter it nor conceal it. If its owner comes along, then give it back to him; otherwise, it belongs to Allaah The Exalted, Who gives it to whomever He wills.'" He goes on to say: "This type is forbidden (to appropriate) because it is associated with the right of someone else; but if the rightful owner is unidentifiable or unknown or one cannot deliver the lost item to him by any possible means, then he is considered legally non-existent and his ownership of the property is nullified as a result according to the scholarly consensus. An example of the absolute inability to return the properties to their rightful owners is the case with unlawful taxes levied by kings and the like and it is known with certainty that they cannot be returned to their rightful owners. In this case, spending this tax money in charity on behalf of the rightful owners is better than leaving them in the hands of the unjust rulers who wrongfully consume them. When this money is spent in charity, it is lawful for the recipients who take it rightfully just as it is unlawful to those who wrongfully consume them (i.e. the unjust rulers who imposed those taxes wrongfully on people)." [Al-Fataawa Al-Kubra]

Allaah Knows best.