He was offering Salah while his lower garment was below his ankles

Q 4: If a man wearing trousers sets out to pray and he is Musbil (one who lengthens and trails clothing below the ankles) and then rolls them up during prayer, is this act included in the prohibition to tuck up garments during prayer? If it is included in the prohibition and he does not roll his clothes, he then becomes Musbil (one who lengthens and trails clothing below the ankles) while praying. Therefore, should he tuck them up or remain Musbil, particularly if he is of the view that Isbaal (lengthening and trailing clothing below the ankles) is prohibited only if done as haughtiness?If one's sleeves are long and one roles them up before praying, is he prohibited to do so? And is Al-Shamagh (traditional Arab head covering) considered clothing which is forbidden to be tucked up? A 4: It is haram (unlawful) for men to wear garments which hang below the ankles, regardless of the type of clothes, i.e. Shirt , garment, underwear or trousers; and regardless of whether the intention of the Musbil is haughtiness or not. According to the general statement of the Prophet Muhammad (peace and blessings of Allah be upon him): The part of an Izar which hangs below the ankles (will cause the person wearing such clothes to be) is in the Fire Recorded by (Part No. 7; Page No. 200

A 4: It is haram (unlawful) for men to wear garments which hang below the ankles, regardless of the type of clothes, i.e. Shirt , garment, underwear or trousers; and regardless of whether the intention of the Musbil is haughtiness or not. According to the general statement of the Prophet Muhammad (peace and blessings of Allah be upon him): The part of an Izar which hangs below the ankles (will cause the person wearing such clothes to be) is in the Fire Recorded by (Part No. 7; Page No. 200)  Al-Bukhari, in his Sahih (Authentic collection of Hadith) and Imam Ahmad, in his Musnad (Hadith compilation) and the statement of the prophet Muhammad (peace and blessings of Allah be upon him): There are three types of people to whom Allah will neither speak on the Day of Resurrection, look at (with compassion), nor purify (of their sins), and they will be tormented severely. They are: One who trails his Izar (garment worn below the waist), one who boasts of kindness shown to another, and one who promotes their business through false oaths. Recorded by Imam Muslim in (his Sahih vol.1, p.102) and Imam Ahmad, in (Al-Musnad)Therefore, one is not permitted to pray while he is Musbil, and he must change these long garments with others that are over the ankles up to the middle of the leg. If he cannot do that, he should roll up his log garments over the ankles before commencing Salah.However, if the worshipper prays while he is Musbil, his prayer is valid per se, but he is sinful for doing what Allah has prohibited and should offer sincere repentance to Allah. It is reprehensible to fold up or roll up one's trousers while praying and the same is true for sleeves, according to what was mentioned in the Two Sahihs (authentic collections) of Hadith (i.e. Al-Bukhari and Muslim) on the authority of Ibn ‘Abbas (may Allah be pleased with them) that the Prophet Muhammad (peace and blessings of Allah be upon him) said: I have been ordered to prostrate myself on seven bones of my body and not to fold up the hem of my garment or hold back my hair during Prayer). What is meant by Al-Kaf in the question is to gather and hem the garments so that they do not fall on the ground while praying. Included in this prohibition is the folding of Al-Shamagh and similar clothes.May Allah grant us success. Peace and blessings of Allah be upon our Prophet Muhammad, his family and companions.