Praise be to Allah.
Firstly, the Muslim must beware of najaasah (impurity) and try to avoid it as much as he can. It was narrated that Ibn ‘Abbaas said: The Messenger of Allaah (peace and blessings of Allaah be upon him) passed by two graves and said, “They are being punished, but they are not being punished for something that was difficult to avoid. One of them used to walk about spreading nameemah (malicious gossip) and the other used not to take care to avoid getting urine on himself.”
Narrated by Muslim, al-Tahaarah, 439
What is meant is that he did not take precautions to avoid getting it on himself. Hence it is permissible to urinate standing up so long as a person can be sure that he will not get splashes of urine on his clothes or his body. See the answer to question no. 9790.
Secondly, with regard to the points raised in the question:
If najaasah (impurity) gets onto a person’s clothes, he does not have to do ghusl, because najaasah is not one of the things that invalidate wudoo’ or ghusl. Rather ghusl is required in the case of major impurity and wudoo’ is required in the case of minor impurity. But what he has to do in this case is to remove the impure material (najaasah).
We are commanded to remove impurity from our clothes because Allaah says (interpretation of the meaning):
“And purify your garments”
And the Prophet (peace and blessings of Allaah be upon him) said, concerning menstrual blood that gets on the clothes, “Take hold of the soiled
place, rub it and put it in water and rub it in order to remove the traces of blood and then pour water over it. Then pray in it.”
If najaasah gets onto something that can be wrung out, then this is what must be done.
2 – Removing the impurity may be done by washing it until the traces of the impurity have disappeared. So if the najaasah gets onto his clothes, he only has to wash the part of the garment where the impurity is, and he does not have to wash the rest of it. Also, he does not have to change his clothes, but if he wants to change his clothes there is nothing wrong with him doing that.
3 – With regard to the ruling on praying in a garment on which there is some impurity, it should be noted that being pure and free from najaasah is a condition of the prayer being valid, and if a person is not free from impurity then his prayer is invalid, because he prayed when he was contaminated with this impurity, So if he prays when he is contaminated with impurity then he has prayed in a manner that is not enjoined by Allaah and His Messenger. It was narrated that the Prophet (peace and blessings of Allaah be upon him) said: “Whoever does an action that is not part of this matter of ours (i.e., Islam), will have it rejected.”
When impurities get onto clothes, one of the following scenarios must apply:
1-When a person is certain that impurity has gotten onto a particular part of his garment, in which case he must wash the area where the impurity is.
2-When he thinks it most likely that the impurity is on a particular part of the garment.
3-When a person thinks that there may be some impurity in some part of the garment. In the second and third cases, he should make a decision, and whatever part of the garment he thinks is affected by the najaasah, he must wash it.
See al-Sharh al-Mumti’ by Ibn ‘Uthaymeen, 2/221
Ruling on a small amount of impurity:
Some of the scholars said that a small amount of impurity cannot be overlooked at all.
Some of them said that a small amount of all types of impurity may be overlooked. This is the view of Abu Haneefah and was the view favoured by Shaykh al-Islam Ibn Taymiyah, especially with regard to problems that many people face, because it is too difficult to be thorough and to clean it properly all the time. Allaah says (interpretation of the meaning):
“and [Allaah] has not laid upon you in religion any hardship”
The correct view is the view of Abu Haneefah and Ibn Taymiyah. Among the small amounts of impurity that may be overlooked because it is too difficult to guard against it is a small amount of urine in the case of one who suffers from incontinence but tries to guard against it as much as he can.
See al-Sharh al-Mumti’ by Ibn ‘Uthaymeen, 1/382
With regard to what constitutes a small amount, whatever ordinary people consider to be a lot is a lot, and whatever they consider to be a little is a little.
On this basis it may be said that the basic principle is that if a few drops of urine get on a person’s garment and he washes off whatever got on it, until he thinks it most likely that the najaasah has disappeared, then whatever is left and is not washed comes under the heading of the small amount of najaasah that may be overlooked, as stated above. And Allaah knows best.
Shaykh Ibn Baaz was asked about the case of one who is unaware of the najaasah. He said:
If he does not find out that it is impure until after he has finished praying, then his prayer is valid, because when the Prophet (peace and blessings of Allaah be upon him) was told by Jibreel whilst he was praying that there was something dirty on his shoe, he did not repeat the first part of his prayer. The same applies if he knows about it (i.e., the impurity) before he prays, then he forgets and prays wearing (the garment with the impurity), and does not remember until after he has finished praying, because Allaah says (interpretation of the meaning):
“Our Lord! Punish us not if we forget or fall into error”
[al-Baqarah 2: 286]
But if he has some doubts whilst praying as to whether there is some impurity on his clothes, it is not permissible for him to stop praying, whether he is leading the prayers or is praying alone; he must complete his prayer.
Fataawa al-Shaykh Ibn Baaz, 12/396-397
4 – The issue of not being sure whether the impurity has been removed: if he gets some impurity on his clothes then this is the certain fact and this certainty will remain until the impurity is removed. Then if he is not sure whether he has removed the impurity or not, he should go by that which is certain, which is that he has not yet removed the impurity. The converse also applies, if he is certain that his clothes are pure, then he is not sure whether something impure got onto them or not, he should go by that which is certain, which is that his clothes are pure because that is what he is certain of.
Shaykh Ibn ‘Uthaymeen said: with regard to a person’s clothes, the basic principle is that they are taahir (pure) so long as he is not certain that some impurity has gotten onto his body or clothes. This basic principle is supported by what the Prophet (peace and blessings of Allaah be upon him) said when a man complained to him that something happened to him during his prayer – i.e., he broke his wudoo’. The Prophet (peace and blessings of Allaah be upon him) said to him: “Do not stop praying unless you hear a sound or detect a smell.” If a person is not sure about it, then the basic principle is that he is taahir (pure). A person may think it is more likely that his clothes have become contaminated with najaasah but so long as he is not certain, the basic principle is that they remain taahir.
Fataawa Ibn ‘Uthaymeen, 11/107
5 – The only thing that is not permissible if a person has najaasah on his clothes is prayer, even if he has not broken his wudoo’. Other actions such as reading Qur’aan etc. are not haraam. And Allaah knows best.