Some scholars also say that the reason for marking lines did not actually exist during the time of the Prophet ﷺ, because the Prophet's masjid was not carpeted.

Also, drawing lines directly on the ground would involve difficulty, since the lines would not remain. As for marking the masjid before each of the five daily prayers, that would involve considerable hardship. Likewise, stretching ropes across the masjid would also involve difficulty, especially in those times, because ropes were expensive and not as readily available as they are today. This is one point. Another point is that ropes would obstruct people as they walked through the masjid. People only needed such markings after masjids began to be covered with carpets. At that point, there was a need to place lines on the carpets, and carpets began to be manufactured with lines already marked on them, which fulfilled the purpose of straightening the rows. In any case, as we have explained, this practice is originally from the category of permissible matters. It is simply a means of straightening the rows, and the means take the ruling of the objectives. What is condemned is introducing new acts of worship. The Prophet ﷺ said: "Whoever introduces into this matter of ours that which is not from it, it will be rejected." What is meant here is introducing acts of worship, not introducing permissible means that help achieve legislated objectives. Such means are not included in the Prophet's ﷺ statement, "Whoever introduces into this matter of ours that which is not from it, it will be rejected." In any case, this issue has been discussed extensively by the scholars, and there has been disagreement among them. Some permitted it, while others prohibited it. It is one of the issues in which scholarly reasoning (ijtihad) is exercised. As for saying that these lines are obligatory, that does not appear to be correct, because straightening the rows can be achieved without them. They are not the only way to straighten the rows. Therefore, they should be regarded as something legislated and permissible, but not as something obligatory, since the rows can still be straightened by other means. However, in our times, people experience difficulty in straightening the rows if such lines are not present, especially in large masjids. When the rows are very long, it becomes difficult to keep them straight. This is unlike smaller masjids, where the rows are short and straightening them is much easier. This was the situation in the Masjid of the Messenger of Allah ﷺ during his lifetime. At that time, it did not have such long and wide rows. But in our time, because masjids are much larger, people face considerable difficulty, especially in large masjids such as Al-Masjid Al-Haram and Al-Masjid An-Nabawi. If people tried to straighten the rows without these lines, they might spend so much time arranging them that the prayer time could pass because of the large number of worshippers. Getting everyone to stand properly and straighten the rows would take a long time, causing hardship and inconvenience for the people. With so many worshippers and such long rows, a person might walk all the way along a row to straighten it, then look back and notice that it has become uneven again. He would then have to return and correct the part that had already passed, and so on. A person may try to straighten one part of the row, then look to the other side and find that it has become uneven. As the saying goes, "He wanted to apply kohl to beautify the eye, but instead made it blind." In other words, he corrects one side only for the other side to become crooked. With long rows, this results in hardship and difficulty. With the great size of today's mosques and the length of the rows, this hardship becomes even greater. In al-Masjid al-Haram, the matter is even more serious. Were it not for the curved lines marked on the floor, people might turn away from the qiblah. Many people could end up praying in a direction other than the qiblah, especially those praying in the outer courtyards. How would they know where the qiblah is? How would they know which direction to face? In those areas, the rows need to curve. If those lines were not marked, many people might pray facing a direction other than the qiblah, and their prayer would become invalid. It is obligatory for the person praying in that location to face the actual direction of the qiblah. If those lines were not there, this serious problem could occur, with people praying in the wrong direction. It is true that someone inside the mosque can usually see the Ka'bah and therefore face it directly. But this is not the case for those praying in the outer courtyards, or in other places where the Ka'bah cannot be seen. If people were left without these lines, this problem would occur, and they would not be able to face the qiblah correctly. So there is clear benefit in these lines. In some places, their benefit is even greater than in others. At the very least, they always provide some benefit. Likewise, because the rows are so wide, they can easily become uneven, and with such large numbers of worshippers there is also considerable hardship. These lines make things easier and simpler. They are not acts of worship in themselves, so it cannot be said that they are religious innovations. Rather, they are only a means—a means of carrying out an act of worship. The act of worship is straightening the rows, while these lines are simply one of the means used to achieve it. A means that helps to fulfil a legislated objective is itself regarded as legislated. This is what appears to be the correct view regarding this issue, and Allah knows best. We have spoken at length about this issue, and time has become short. So we will stop at what we have read up to this point. And all praise is for Allah. Source: https://t.me/madrasatunaa/494