Ahmad ibn Muhammad ibn ‘Isa narrated from al-Hasan ibn Mahbub and Ali ibn al-Hakam, both from Abu Yahya al-Hannat. He said: I asked Abu Abdillah عليه السلام, about praying the supererogatory prayers during the day while on a journey. Imam عليه السلام said: “O my son, if the nawafil (supererogatory prayers) during travel were valid, then the obligatory prayer would have remained complete (four rak’ahs).”