Explanation:

Section 25(2) of the Indian Contract Act – 
25. Agreement without consideration, void, unless it is in writing and registered or is a promise to compensate for something done or is a promise to pay a debt barred by limitation law.
An agreement made without consideration is void, unless- (1) It is expressed in writing and registered under the law for the time being in force for the registration of documents, and is made on account of natural love and affection between parties standing in a near relation to each other; or unless. (2) It is a promise to compensate, wholly or in part, a person who has already voluntarily done something for the promisor, or something which the promisor was legally compellable to do; or unless. (3) It is a promise, made in writing and signed by the person to be charged therewith or by his agent generally or specially authorised in that behalf, to pay wholly or in part debt of which the creditor might have enforced payment but for the law for the limitation of suits. In any of these cases, such an agreement is a contract.