Mishkat al-Masabih 3 Purification كتاب الطهارة 218

وَعَن صَفْوَان بن عَسَّال قَالَ: كَانَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ يَأْمُرُنَا إِذَا كُنَّا سَفَرًا أَنْ لَا نَنْزِعَ خِفَافَنَا ثَلَاثَةَ أَيَّامٍ وَلَيَالِيَهُنَّ إِلَّا مِنْ جَنَابَةٍ وَلَكِنْ مِنْ غَائِطٍ وَبَوْلٍ وَنَوْمٍ. رَوَاهُ التِّرْمِذِيّ وَالنَّسَائِيّ

Safwan b. ‘Assal said, “God’s messenger used to command us, when we were travelling, not to take off our shoes for three days and nights except for seminal defilement, and not to do so on account of easing ourselves, passing water, or sleeping.” Tirmidhi and Nasa’i transmitted it.