Ruling on praying with pant legs rolled up

Firstly: 

There are a number of hadeeths which forbid rolling up the
garment when praying. 

Al-Bukhaari (812) and Muslim (490) narrated from Ibn ‘Abbaas
(may Allah be pleased with him) that the Messenger of Allah (blessings and
peace of Allah be upon him) said: “I have been commanded to prostrate on
seven bones: the forehead – and he pointed to his nose – the hands, the feet
and the ends of the feet (i.e., toes), and not to tuck up my garment or
hair.” 

Tucking up the garment or hair means gathering it together to
prevent it falling on the floor when one prostrates. 

An-Nawawi said: 

The scholars are unanimously agreed that it is not allowed to
pray with the garment, sleeves and so on rolled up. … All of that is not
allowed according to scholarly consensus; it is makrooh in the same that it
is discouraged, so if a person prays like that he has done something wrong
but his prayer is still valid. Abu Ja‘far Muhammad ibn Jareer at-Tabari
quoted as evidence scholarly consensus. Ibn al-Mundhir narrated that the one
who does that should repeat his prayer, and he narrated this view from
al-Hasan al-Basri. End quote. 

It says in Tuhfat al-Minhaaj, 2/161-162: 

It is makrooh for the one who is praying to tuck up his hair
by putting it together or putting it under his headgear, or to tuck up his
garment, such as rolling up his sleeve or hem. End quote. 

Based on that, tucking or rolling the pants up is makrooh
when praying. 

Secondly: 

There are ahaadeeth which forbid letting the garment hang
down or come lower than the ankles (isbaal). 

Al-Bukhaari (5787) narrated from Abu Hurayrah (may Allah be
pleased with him) that the Prophet (blessings and peace of Allah be upon
him) said: “Whatever of the izaar comes lower than the ankles is in the
Fire.” 

Abu Dawood (4084) narrated from Abu Juray Jaabir ibn Sulaym
(may Allah be pleased with him) that the Prophet (blessings and peace of
Allah be upon him) said: “Beware of letting the garment come below the
ankles, for that is conceit and Allaah does not like conceit.”

Classed as saheeh by al-Albaani in
Saheeh Abi Dawood 

So it is not permissible for a man to make his garment so
long that it comes below the ankles. If he insists on letting it come below
the ankles and wants to pray wearing these pants, then if he leaves them as
they are he will be praying with his garment coming below the ankles, and if
he rolls them up to come above the ankles, he will be praying with his
garment tucked up. In this case we have a conflict between two prohibitions:
the prohibition on letting the garment come below the ankle and the
prohibition on rolling up the garment when praying. There is no doubt that
the ruling on letting the garment come below the ankle is more stringent,
because that is a major sin. As for rolling up the garment when praying, it
is makrooh (disliked). If there is a conflict then precedence must be given
to that which is more important, which is avoiding letting the garment come
below the ankle. In that case he should roll up his garment until it comes
above the ankle. 

Shaykh ‘Abd ar-Rahmaan as-Suhaym was asked: 

I tuck up my pants when praying so that I will not be letting
them come below the ankles, but the Prophet (blessings and peace of Allah be
upon him) forbade tucking up the garment when praying. Does this apply to
tucking up the pants? What is the ruling on that? 

He replied: 

If the pants or trousers come below the ankle, then they must
be lifted up, in prayer or otherwise. In fact it is not permissible for them
to touch the ankle because the Prophet (blessings and peace of Allah be upon
him) said: “The izaar (lower garment) should come to mid-calf, but if you
insist it may come lower, and if you insist it may come to the bottom of the
calf, but it should not touch the ankles.”

Narrated by Imam Ahmad and an-Nasaa’i. 

Tucking up the pants does not come under this prohibition
because lifting the izaar away from the ankles is a shar‘i requirement; in
fact it is obligatory, whereas the prohibition on tucking up the garment or
the hair signifies that it is makrooh (disliked).

End quote. 

Thirdly: 

With regard to a woman praying in rolled up pants, women are
forbidden to pray wearing pants whether they are rolled up or otherwise. 

If she goes against that and prays wearing pants, the prayer
is valid in and of itself. 

An-Nawawi (may Allah have mercy on him) said in al-Majmoo‘
(3/176): If it covers the colour (of the skin) but shows the shape of the
body such as the knee and buttock, and the like, then the prayer is valid
because the condition of covering the body was fulfilled. ad-Daarimi and the
author of al-Bayaan narrated a view that it is not valid if it shows
the shape, but this is an obvious mistake. End quote. 

For more information please see the answer to question no.
46529 

If a woman prays wearing pants, she should not roll them up
because there is no need for that, as what she is required to do is to cover
the tops of her feet when praying, and because the prohibition on making the
garment longer then the ankles applies only to men and does not include
women. 

And Allah knows best.