Musannaf Ibn Abi Shayba 3:3184

Abu Khalid al-Ahmar narrated to us, from Hajjaj, from ‘Ata’, and from al-Qasim, from Mujahid, regarding [the verse]: "And when the prayer has been concluded, disperse within the land," they both said: If he wishes, he may do so, and if he wishes, he may not do so.