Sayyiduna Uqbah bin Amir (may Allah be pleased with him) said: The Noble Prophet (peace and blessings be upon him) said: "The guarantee for a slave is for three days."
Qatadah (may Allah have mercy on him) explained its interpretation as follows: If a defect is found in the slave on the third day, the buyer has the option to return him without any proof, but if a defect is found after four days, he cannot return him without proof.