Praise be to Allah.
It is permissible for a worshipper to use a tissue in this case. The scholars (may Allah have mercy on them) stated that it is permissible to make some slight movements during prayer if the worshipper needs to do so, as it says in al-Majmoo’ by al-Nawawi (4/94). They quoted as evidence many ahaadeeth that were narrated from the Prophet (peace and blessings of Allah be upon him). For example, Abu Dawood (650) narrated that Abu Sa’eed al-Khudri said: “Whilst the Messenger of Allah (peace and blessings of Allah be upon him) was leading his companions in prayer, he took off his shoes and placed them to his left. When the people saw that, they took off their shoes too. When the Messenger of Allah (peace and blessings of Allah be upon him) finished his prayer he said, ‘What made you take off your shoes?’ They said, ‘We saw you taking off your shoes so we took off ours too.’ The Messenger of Allah (peace and blessings of Allah be upon him) said, ‘Jibreel (peace be upon him) came to me and told me that there was something dirty on them [my shoes].’ And he said, ‘When any one of you comes to the mosque, let him look at his shoes and if there is anything dirty on them, let him wipe it off and pray in them.’” (Classed as saheeh by al-Albaani in Saheeh Abi Dawood, 605). Al-Khattaabi (may Allah have mercy on him) said in Ma’aalim al-Sunan (2/329): this shows that a slight movement does not affect one’s prayer.
If a person needs to wipe his nose whilst praying, such as one who has a cold or flu, it is o.k. for him to take a tissue out and wipe his nose. A report was narrated from the Prophet (peace and blessings of Allah be upon him) which indicates that this movement in prayer is permissible. Muslim (855) narrated from Abu Hurayrah (may Allah be pleased with him) that the Messenger of Allah (peace and blessings of Allah be upon him) saw a glob of phlegm in the qiblah of the mosque. He turned to the people and said, “What is wrong with any one of you who stands before his Lord and expectorates in front of Him? Would any one of you like it if someone were to stand in front of him and expectorate in his face? If any one of you needs to expectorate, let him spit to his left, under his shoe. If he cannot do that, then let him do like this – ” then he spat onto his garment and rub part of it against another part.
Should he wipe his nose with his right hand or his left hand?
The answer is that he should wipe it with his left hand, because in Islam the right hand is only for things that are regarded as honourable, and the left hand is for things that are regarded as unclean.
Al-Bukhaari (163) and Muslim (395) narrated that ‘Aa’ishah said: “The Prophet (peace and blessings of Allah be upon him) liked to start with the right when putting on his shoes, combing his hair, purifying himself and in all his affairs.”
Abu Dawood narrated that ‘Aa’ishah also said: “The right hand of the Messenger of Allah (peace and blessings of Allah be upon him) was for his purification and food, and his left hand was for cleaning himself after using the toilet and for everything that was unclean.” (Classed as saheeh by al-Bukhaari in Saheeh Abi Dawood, 26).
Al-Nawawi (may Allah have mercy on him) said in Sharh Saheeh Muslim (1/160): “This is a recurring principle in sharee’ah. Whatever has to do with honourable things, such as putting on clothes, trousers and socks, entering the mosque, using the miswaak (tooth-stick), applying kohl, clipping the nails, trimming the moustache, combing the hair, plucking the armpit hairs, shaving the head, saying salaam at the end of the prayer, washing the limbs in wudoo’, coming out of the toilet, eating and drinking, shaking hands, acknowleging the Black Stone, and so on, it is mustahabb to use the right hand or start on the right. With regard to things that are the opposite, such as entering the toilet, exiting the mosque, wiping one’s nose, cleaning oneself after using the toilet, taking off one’s clothes, trousers and socks, etc., it is mustahabb to use the left hand or start on the left. All of that is because of the status of the right hand. And Allah knows best.