Bulugh al-Maram 61
Narrated Safwan bin ‘Assal (rad):
When we were on a journey, the Prophet (ﷺ) used to command us to wear our leather socks for three days and three nights, whether we had to answer the call of nature or slept. However, in case of ejaculation or sexual impurity, he commanded us to remove the leather socks. [Reported by An-Nasa’i and At-Tirmidhi, version is of the latter. With them Ibn Khuzaima graded it Sahih (sound)].
وَعَنْ صَفْوَانَ بْنِ عَسَّالٍ ‏- رضى الله عنه ‏- قَالَ: { كَانَ رَسُولُ اَللَّهِ ‏- صلى الله عليه وسلم ‏-يَأْمُرُنَا إِذَا كُنَّا سَفْرًا أَنْ لَا نَنْزِعَ خِفَافَنَا ثَلَاثَةَ أَيَّامٍ وَلَيَالِيَهُنَّ, إِلَّا مِنْ جَنَابَةٍ وَلَكِنْ مِنْ غَائِطٍ, وَبَوْلٍ, وَنَوْمٍ }  أَخْرَجَهُ النَّسَائِيُّ, وَاَلتِّرْمِذِيُّ وَاللَّفْظُ لَهُ, وَابْنُ خُزَيْمَةَ وَصَحَّحَاه ُ  1‏ .‏‏1 ‏- حسن.‏ رواه النسائي (1/83‏-84)‏، والترمذي (96)‏، وابن خزيمة (196)‏، وقال الترمذي: حسن صحيح.‏