Putting lines in the mosque to make the rows straight
Question

                What is the ruling on putting lines in the mosques so that it will be easy for the worshippers to make the rows straight? I heard that this is bid’ah (an innovation).
Praise be to Allah.
    The command to make the rows straight was narrated in many 
    well-known ahaadeeth, including the words of the Prophet  (peace and 
    blessings of Allaah be upon him): “Make your rows straight, for 
    straightening the rows is part of perfecting the prayer.” Narrated by 
    al-Bukhaari (723) and Muslim (433) from the hadeeth of Anas (may Allaah be 
    pleased with him). 

    And he  (peace and blessings of Allaah be upon him) said: 
    “Either you straighten your rows or Allaah will create discord among you.” 
    Narrated by al-Bukhaari (717) and Muslim (436) from the hadeeth of 
    al-Nu’maan ibn Basheer (may Allaah be pleased with him). 

    Some scholars are of the view that it is obligatory to make 
    the rows straight, because when the Prophet  (peace and blessings of 
    Allaah be upon him) saw a man whose chest was sticking out (from the row) he 
    said: “Slaves of Allaah! Make your rows straight or Allaah will cause 
    discord among you.” This is a warning, and there is no warning except with 
    regard to a haraam action or failure to do an obligatory action. The view 
    that it is obligatory to straighten the rows is a strong view. End quote 
    from Fataawa al-Shaykh Ibn ‘Uthaymeen (13/question no. 375). 

    So the imam should tell the people to straighten the rows, 
    and he should take care of that. 

    As for putting lines on the mats or carpets to help make the 
    rows straight, there is nothing wrong with that, and it is not an 
    innovation. 

    The scholars of the Standing Committee were asked: What is 
    the ruling on making lines on the mats or carpets in the mosque, because the 
    qiblah is not square with the building, to help organize the rows? 

    They replied: There is nothing wrong with that, and if they 
    pray without a line there is nothing wrong with that either, because a 
    slight deviation from the qiblah does not matter. 

    Fataawa al-Lajnah al-Daa’imah 
    (8/15). 

    Shaykh ‘Abd al-Razzaaq ‘Afeefi (may Allaah have mercy on him) 
    was asked about the ruling on drawing lines in the mosques to make the rows 
    straight. 

    He replied: If the people cannot make their rows straight 
    except by means of that, there is nothing wrong with that, or if the mosque 
    was built slightly off from the qiblah and the rows cannot made be straight 
    except by means of that, there is nothing wrong with it in sha Allaah. End 
    quote from Fataawa wa Rasaa’il al-Shaykh ‘Abd al-Razzaaq ‘Afeefi (p. 
    412). 

    And Allaah knows best.