He has polio and he does not pray in congregation sometimes

Praise be to Allah.

Praying in congregation is obligatory for men who are able for it, whether they are in their home town or travelling, according to the more correct of the two scholarly opinions, because of a great deal of evidence, which has been quoted in the answers to questions no. 8918 and 120. 

If you are able to go to the mosque, then praying in congregation is obligatory for you. You said that you usually pray in the mosque, praise be to Allaah. This by the grace of Allaah and His blessing to you. So strive to show gratitude for it, for gratitude increases the blessing, as Allaah says (interpretation of the meaning): 

“If you give thanks (by accepting Faith and worshipping none but Allaah), I will give you more (of My Blessings)”

[Ibraaheem 14:7]. 

Secondly: 

Sleeping is a (valid) excuse for not praying in congregation, so long as it is not due to carelessness, such as staying up at night for no need and not making use of the means to help one wake up. Al-Tirmidhi (177), al-Nasaa’i (615), Abu Dawood (437) and Ibn Maajah (698) narrated that Abu Qataadah (may Allaah be pleased with him) said: They told the Prophet (peace and blessings of Allaah be upon him) about their sleeping and missing the prayer, and he said: “There is no negligence when one is sleeping, rather there is negligence when one is awake. If any one of you forgets to pray, or sleeps and misses a prayer, then let him pray when he remembers.” Classed as saheeh by al-Albaani in Saheeh al-Tirmidhi. This hadeeth is also narrated in al-Saheehayn with similar wording. 

Al-Mubaarakfoori said in Sharh al-Tirmidhi: “There is no negligence when one is sleeping” means that negligence cannot be ascribed to the one who sleeps and delays a prayer as a result. 

“rather there is negligence when one is awake” means that negligence and shortcomings are committed by the one who is awake and fails to pray or delays the prayer with no excuse. End quote. 

The Standing Committee for Issuing Fatwas was asked: A man prayed Fajr after the sun had risen, and that became his habit every day for two years, because he claimed that sleep overtook him, as he stayed up at night in cafes and watching entertainment until after midnight. Is his prayer valid? 

They replied: It is haraam to delay prayers until after the time for them is over. The adult Muslim must offer prayers on time – Fajr prayer and others – by asking someone to wake him up for them or by using an alarm clock to wake him up. It is haraam for him to stay up late watching entertainment etc as Allaah has forbidden him to stay up late doing things that will prevent him from offering Fajr prayer on time or in congregation. The Prophet (peace and blessings of Allaah be upon him) forbade staying up after ‘Isha’ for no legitimate shar’i reason. Every deed that will cause a delay in praying until the time for the prayer is over is haraam, unless an exception is made in sharee’ah. End quote from Fataawa al-Lajnah al-Daa’imah (6/15). 

Thirdly: 

If you stay away from offering Zuhr prayer in congregation for a valid reason, such as not being able to go to the mosque, there is no sin on you. But if there is no excuse then you have to repent to Allaah and offer the prayer in congregation in the future. 

We ask Allaah to help you to do that which He loves and which pleases Him. 

And Allaah knows best.