It is required for its validity to intend from the night, or an intention concurrent with the dawn; because this fasting is not specified, so it must be intended until it becomes specified, as mentioned in Sharh al-Wiqayah p.234, and 'Umdat al-Ri'ayah 1: 307. Therefore, if one fasts with the intention after dawn, it becomes voluntary, and he must make up for this voluntary fast if it is invalidated.