Hafs bin Asim bin Umar bin Khattab (may Allah have mercy on him) narrates that he asked Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) about not offering voluntary (nafl) prayers during travel. Sayyiduna Abdullah (may Allah be pleased with them both) replied, "If I were to offer voluntary prayers, then I would have completed my obligatory prayers." Imam Zuhri says that he asked Hazrat Salim, "Did you ask Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) the same question that Hafs bin Asim asked him?" Hazrat Salim replied, "No, indeed we used to fear asking him about some issues." Imam Abu Bakr (may Allah have mercy on him) says that the narrations of Salim and Hafs indicate that the narration of Atiyyah bin Sa’d from Sayyiduna Ibn Umar (may Allah be pleased with them both) is mistaken. And Ibn Abi Layla made a mistake in combining Nafi’ and Atiyyah in narrating from Sayyiduna Ibn Umar (may Allah be pleased with them both) regarding voluntary prayers during travel. However, this issue belongs to the same category about which we have already stated that the denial of something by a narrator cannot be taken as evidence against its affirmation. If Sayyiduna Ibn Umar (may Allah be pleased with them both) did not see the Prophet (peace and blessings be upon him) offering voluntary prayers during travel, then other companions did see the Prophet (peace and blessings be upon him) offering voluntary prayers during travel. Therefore, preference will be given to the hadith of the companion who saw the Prophet (peace and blessings be upon him) (performing voluntary prayers), not to the narration of the companion who did not see the Prophet (peace and blessings be upon him) (offering voluntary prayers during travel). I have mentioned this issue at several places in my books.