1649/1 - Abu Hurayrah (may Allah be pleased with him) reported that the Prophet (may Allah’s peace and blessings be upon him) said: “None of you should walk wearing one shoe. He should either wear both of them or take them both off.”
-- [Narrated by Al-Bukhāri and Muslim]
1650/2 - He also reported that he heard the Prophet (may Allah’s peace and blessings be upon him) say: “If the strap of the sandal of one of you breaks, let him not walk in the other sandal until he fixes it.” [Narrated by Muslim]
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1) It is prohibited to walk with one foot in a shoe and the other without. This constitutes injustice towards the body parts. It behooves us to treat them justly and give each part its due right; otherwise, we will be at fault.
2) Walking barefooted occasionally, without the intent to draw people’s attention, is part of the Prophet’s guidance, as he forbade undue luxury and used to command the people to walk barefooted from time to time.
1651/3 - Jābir (may Allah be pleased with him) reported: “The Messenger of Allah (may Allah’s peace and blessings be upon him) forbade that a man should wear his shoes while standing.”
[Narrated by Abu Dāwūd with a sound Isnād]
1) It is disliked to wear shoes while standing lest one should fall and hurt himself.
2) Islam pays attention to the proper etiquettes, so that Muslims appear in the best condition and form.
The prohibition related to wearing shoes while standing applies to such shoes that need some effort to let one’s feet in them. If he wears it while standing, he may lose his balance and fall. As for other shoes that need no effort and can be worn without fear of harm, there is nothing wrong if people put them on while standing. They do not fall under the prohibition in question.