What is the ruling on praying in trousers without wearing a shirt, and the reverse?

The questioner : What is the ruling on wearing only trousers without a shirt in prayer, or wearing only a shirt without trousers?

The Shaykh : As for the second matter, there is no issue if the shirt covers the awrah (part of the body that must be covered). As for praying in trousers, the one praying is in one of two situations:
The first is that he finds nothing but the trousers, and with these trousers he covers his awrah (part of the body that must be covered); in that case, his prayer is valid.
However, if he finds something to cover the upper part of his body as well, he must do so and must not enter prayer with his upper body, including his shoulders, chest, and back, exposed. This is not because that is an awrah (part of the body that must be covered) outside of prayer, but because it is among the obligations of prayer and the etiquettes of prayer that Allah (Blessed and Exalted is He) has made obligatory through the tongue of His Prophet (peace and blessings be upon him). He said, in what Abu Dawud narrated in his Sunan from the hadith of Ibn Umar (may Allah be pleased with him): The Messenger of Allah (peace and blessings be upon him) said: . Whoever has an izar (lower garment) that covers the upper part of his body and a rida' (upper garment) that covers the lower part of his body, let him do so; let him wear the izar and the rida'. For Allah has more right to be adorned for than anyone else. In fact, the Prophet (peace and blessings be upon him) indicated explicitly that whoever has an izar and does not wear it, but only prays covering his awrah (part of the body that must be covered), his prayer is not valid. That is his saying (peace and blessings be upon him): . This Prophetic command that you heard in the hadith of Ibn Umar, and this prohibition that came in the second hadith—which is from the hadith of Abu Hurayrah—is a matter that many people do not know, especially the pilgrims and those performing Umrah. I saw today a man praying in the mosque by the seashore with his right shoulder exposed, wearing an izar and a rida'. I realized he was performing Umrah, so I approached him and said: It appears you are intending to perform Umrah? He said: Yes. I reminded him that his exposing his right shoulder now, before he arrives in Makkah, is first contrary to the Sunnah, because exposing the right shoulder, which is known in the language as idhtiba', is only for the arrival tawaf (circumambulation of the Ka'bah). As for when the one in ihram (the consecrated state of pilgrimage) enters ihram from his miqat (the boundary at which ihram is entered), it is not permissible for him except to cover his entire body with his garment. As for intentionally exposing his shoulder in advance, that is a religious innovation (bid'ah) in which the majority of pilgrims and those performing Umrah have fallen. We see them doing so every year, and I have seen many of them do this, the last of whom was this man today. I reminded him that he had fallen into two violations: the first is that he exposed his shoulder while he had not yet arrived in Makkah, and this is not permissible because it is contrary to the Sunnah. The more serious matter is that you prayed while your shoulder was exposed. I reminded him of the previous hadith, namely the saying of the Messenger of Allah (peace and blessings be upon him): . It was a surprise for this poor man, and he said something of no benefit: "I am performing Umrah." And I said to him: You are performing Umrah, but you must do such and such. He said: May Allah reward you with good. He got in the car and left as he had been before.
It is hoped that you will pay attention to this ruling and remind others, because people are in great and severe negligence, especially when we see them sa'y (walking between al-Safa and al-Marwah) between al-Safa and al-Marwah with their shoulders exposed. This is contrary to the Shari'ah (Islamic sacred law), and when they stand for prayer, they pray and expose their prayer to invalidity.
This is what should be mentioned on this occasion.