Is her prayer valid when she is wearing a diaper in which there is impurity (najasah)?

Firstly:

In order for prayer to be valid, it is stipulated that the clothes and body, and the place in which one is praying, must be pure (tahir), and it is not permissible for the worshipper to pray when he is wearing a garment that is contaminated with impurity.

Allah, may He be exalted, says (interpretation of the meaning): {And your clothing purify} [al-Muddaththir 74:4].

Abu Dawud (650) narrated that Abu Sa`id al-Khudri (may Allah be pleased with him) said: Whilst the Messenger of Allah (blessings and peace of Allah be upon him) was leading his companions in prayer, he took off his sandals and placed them on his left. When the people saw that, they took off their sandals too. When the Messenger of Allah (blessings and peace of Allah be upon him) finished his prayer, he said: “What made you take off your sandals?” They said: We saw you take off your sandals, so we took off our sandals too. The Messenger of Allah (blessings and peace of Allah be upon him) said: “Jibril (blessings and peace of Allah be upon him) came to me and told me that there was some dirt (impurity) on them.” And he said: “When one of you comes to the mosque, let him check and if he sees any dirt or filth (impurity) on his sandals, let him wipe them and pray in them.” Al-Albani classed it as authentic in Sahih Abi Daud.

It says in Zad al-Mustaqni`: Whoever carries impurity on him that cannot be overlooked, or finds it on his garment or his body, his prayer is not valid.

Shaykh Ibn `Uthaymin (may Allah have mercy on him) said in his commentary: “Whoever carries impurity on him that cannot be overlooked”: from the words “that cannot be overlooked” we may understand that some impurities may be overlooked, and that is indeed so. The author stated previously that a small amount of blood may be overlooked, if it comes from a pure (tahir) living being, such as a human for example, or the blood of a sheep, camel and the like. He also stated previously that Shaykh al-Islam [Ibn Taymiyah – may Allah have mercy on him] thought that a small amount of all impurities may be overlooked, especially if it is difficult to avoid them, as in the case of those who own donkeys and rides them a great deal, for whom it is not possible to avoid drops of the donkey’s urine sometimes, if not most of the time. Thus Shaykh al-Islam thought that the reason (for overlooking it) is the difficulty in avoiding it, so whenever it is too difficult avoid the impurity, a small amount of it may be overlooked. The same may be said in the case of painters, that a small amount of paint may be overlooked if it gets onto their bodies and prevents water from reaching their skin [when doing wudu’], because religion is easy, and such things often happen to a person without him realising sometimes, or he realises but it is difficult for him to avoid it.

So with regard to carrying impurity, if it contaminates a person’s garment, then in fact he is carrying it, because he is wearing a garment that is impure (najis). If he puts the impurity in a bottle in his pocket, then he is carrying impurity that cannot be overlooked. This sometimes happens nowadays, when if a person wants to test his stools or urine, he puts it in a bottle and may be carrying it [in his pocket] when he is praying. This prayer is not valid, because he is carrying impurity that cannot be overlooked. End quote from ash-Sharh al-Mumti` (2/22).

So if someone prays wearing a diaper in which there is some impurity, and he knows that the impurity is there and remembers it, his prayer is not valid, unless he is incontinent. Regarding matters related to incontinence, please see the answers to questions no. 106751 and 126293.

Secondly:

The individual must purify himself from impurities, as mentioned above. If he cannot do that, and he can afford it, he must hire someone to cleanse himself, because what is essential to doing an obligatory action is also obligatory. If he cannot afford to hire someone, because he is not well off or there is no one who can do that, then he must pray as he is, for Allah does not place on any soul a burden greater than it can bear.

It says in Kashshaf al-Qina` (1/102): If an amputee or someone in a similar situation, such as one who is paralyzed or sick and unable to do wudu’ by himself, can find someone to help him do wudu’ or ghusl in return for payment at the normal rate, and he is able to afford that without causing hardship to himself or to those on whose maintenance he is obliged to spend, then he must do that, because he comes under the same heading as one who is healthy. If he can find someone to help him do tayammum but is not able to find someone to help him do wudu’ or ghusl, then he must do that, as in the case of a healthy person who is able to do tayammum but not wudu’. If he cannot find anyone to help him do either wudu’ or tayammum, and he cannot afford to hire someone or cannot find someone to hire, then he must pray as he is. It says in al-Mughni: I do not know of any difference of opinion regarding that. Similarly, if he cannot find anyone except by paying more than the usual fee, unless the increase [for helping him to do wudu’ or ghusl] rather than tayammum is small, then he should pray as he is, and he does not have to repeat his prayer, as in the case of one who has neither of the means of purifying himself [that is, water for wudu’ or dust for tayammum]. What is mentioned above regarding wudu’ also applies in the case of cleaning oneself after relieving oneself (istinja’). If someone volunteers to help him purify himself, then he must accept that. It says in al-Furu`: Rather he does not have to do that [accept such help], and he may do tayammum instead. (End quote)

Thirdly:

The woman asked about here must do one of two things:

Firstly: doing without the diapers, by placing a vessel or the like near her in which she can relieve herself and clean herself with water or even with tissues and the like;

Secondly: taking off the diaper and cleansing herself from impurity before praying.

If neither option is possible, even by hiring someone to empty the vessel or change the diaper, and no one volunteers to do that, she may pray with the impurity, and she is excused.

And Allah knows best.