Putting lines in the mosque to make the rows straight

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.