By what instrument of law did the daughter sell 1 acre of land to a third party when the same was legally not transferred to her? As per your own statement of facts, the land given to her at the time of her marriage was not documented, which resultantly means that she had not become the owner of this land. Hence, she could not have sold the land of which she was not the owner. Whether any deed/agreement was made between the daughter and her brother and mother?

Since the land given to daughter at the time of her marriage was not a transfer of land in the eyes of law she can now claim her share i.e 1/3rd share in the remaining land. Son also has 1/3rd share in the land which he can cull out by filing a case for partition.

The widow mother also has an equal share in the property.

You have not answered as to by what instrument the daughter sold the property and created third party rights. This assumes significance in view of the fact that she alone could not have made the sale deed.

If son has sold and gifted property beyond his own share therein i.e 1/3rd share then such a transfer is illegal and can be cancelled on a legal action being brought by sister or mother. The daughter can move to court and get the sale deed and gift deed cancelled in as much as the transfer of property infringes her own proprietary rights. The court may cancel the transfer of property. It is a fundamental principle of law that nobody can sell a property beyond his own share therein.

1) as rightly pointed out by Mr Davesar daughter could not have sold 1 acre of land . no gift deed was made nor land transferred in her name . without consent of other legal heirs daughter could not have sold 1 acre of land

2) daughter would have 1/3rd share in 3 acres of land .

3) son cannot sell or transfer or create third party rights in balance land without consent of his mother /sister . gift in favour of his daughter and sale to third party can be challenged by other legal heirs if it is more than his 1/3rd share

was payment received in daughter name? was it by cheque?

In the earlier part of your query you had mentioned that daughter has sold the property, whereas now you have stated that mother son duo sold the property. Be that as it may, there is a cloud over the transfer of property in as much as even mother and son could not have made the sale deed. Although without a threadbare perusal of the related documents it is not possible to say anything concrete, nonetheless it is possible that the ownership may not have even passed to the purchaser, which may open the floodgates of litigation by the purchaser.

If son believes himself to be the victim of fraud/cheating then he should move to court and file a case for cancelling the transfer of land made by daughter and also to cull out his own share therein.

How are they trying to cheat the court if no litigation respecting the land in question is pending in any court?

If the amount was paid in cash then the property cannot be said to have been sold by the daughter.

on paper all three of you sold the property not daughter alone. so as on today legally she has 1/3 of share in left over property

it cannot be said property was sold by daughter only . you have no evidence of payment made to daughter . your case that 1 acre was sold by daughter is not borne by facts on record .

thanks for your appreciation . best course fpr you is to involve family elders to reason with your sister

Deed of family settlement should be prepared . get it duly stamped and registered .