Is Praying in Congregation at Home Rewarded?
Question

Praying with the second or third Jamma in a mosque has equivalent reward (25 or 27) with praying with the Imam for the first time? or praying with a group of 5-10 people at work/school enable to get the same reward with those prayed in the mosque?.
Praise be to Allah.Is praying in congregation obligatory?
Praying in congregation is obligatory . This is what is indicated by the Shar`i evidence from the Quran and Sunnah. As Allah has enjoined prayer in congregation in the battlefield, so it is more appropriate that it is obligatory at times of stability and peace.
Is it obligatory to pray in the mosque?
 It is obligatory to pray in congregation in the mosque , not in workplaces or schools.
This applies if the Muslim is accountable, male, able to do it and can hear the Adhan without the aid of a loudspeaker.
This is indicated by the fact that the Prophet (peace and blessings of Allah be upon him) thought of burning down the houses of those who prayed at home , even though they may have prayed in congregation.
Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (peace and blessings of Allah be upon him) said: “I was thinking of ordering that the Iqamah for prayer be given, then I would tell a man to lead the people in prayer, and I would set out with men carrying bundles of firewood, and go to people who do not attend the prayer and burn their houses down around them.” (Narrated by Al-Bukhari, 657 and Muslim, 651)
This has been discussed in the answer to question no. 72398 .
Hence there is no comparison between prayer in congregation at home and prayer in congregation in the mosque . The reward and virtue come from praying in congregation in the mosque. The one who does not pray in congregation in the mosque and chooses to pray in congregation at home or in the workplace does not attain the reward of praying in congregation in the mosque, if he is free from sin in the first place.
Is it rewarded to pray in congregation at home for an excuse?
The one who has an excuse for not attending prayer in congregation in the mosque will have the same reward as those who pray in congregation, even if he prays at home.
Excuses for not praying in congregation in the mosque
A Muslim may be excused for not praying in congregation in the mosque, such as if he is far away and the sound of the Adhan in its natural form does not reach him, or he is sick, or afraid. If that is the case, then he should pray in congregation with the members of his family who are not obliged to pray in congregation, or those who have a similar excuse. Here it is valid to differentiate between the congregation in the mosque and the congregation of these people in terms of numbers.
The congregation that is greater in number is more beloved to Allah – and we shall quote the relevant Hadith below – but there is no room for comparison of other rewards, such as the number of steps that the worshipper takes to the mosque, or coming early to pray, and Allah preparing a welcome in Paradise every time he comes and goes, and so on.
These rewards are denied to the one who prays in his house, unless he is one who regularly prays in the mosque but is kept from doing so by sickness or some other reason, in which case a reward will be decreed for him like that which he used to do, as is stated in an authentic Hadith from the Prophet (peace and blessings of Allah be upon him).
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
“For the one who is excused, the reward will be decreed if it was his habit to pray in congregation, because the Prophet (peace and blessings of Allah be upon him) said: “If a person falls sick or travels, there will be decreed for him a reward like that for what he used to do when he was healthy or not travelling.”” (End quote from Ash-Sharh Al-Mumti`, 4/323)
If a man does not have anyone to pray with, he may pray alone, but the more people who pray, the dearer that is to Allah.
Is it sinful to deliberately miss the first prayer in congregation? 
If a person deliberately misses the first prayer in congregation , he is sinning, but his praying in congregation is better than his praying alone, although he will not have the reward of the first congregational prayer.
Those who delay it without any excuse and aim to pray with the second or third congregational prayer – as happens in some marketplace mosques – are sinning by deliberately missing the first congregational prayer, and they are deprived of the reward even if they pray in congregation with a group that is larger than the first congregational prayer.
Shaykh Ibn `Uthaymin (may Allah have mercy on him) said:
“As for the view of those who say that if they pray in the mosque, even if that is after the first congregational prayer, they will have the twenty-seven-fold reward, this is not correct. The twenty-seven-fold reward applies only to the first congregational prayer. As for the second congregational prayer, undoubtedly praying in congregation is better than praying individually, because the Prophet (peace and blessings of Allah be upon him) said concerning a man who entered the mosque and had missed the prayer: “Who will give charity to this man and pray with him?” and one of the people got up and prayed with him. And he (peace and blessings of Allah be upon him) said: “A man’s praying with two other men is better than his praying with one other man, and the more there are, the more beloved that is to Allah, may He be Glorified and Exalted.” But as for the second congregational prayer  attaining the same reward as the first, this is not correct. Otherwise people would go to the mosque whenever they wanted, and they would pray in congregation and say, We have gotten the twenty-seven-fold reward. But I do not know of anyone who says that, i.e., that the second prayer is like the first in terms of attaining the twenty-seven-fold reward. I do not know of anyone who says this.” (End quote from Liqa’ Al-Baab Al-Maftuh, 44/question no. 10)
Could not catch the first congregation for an excuse; will one be rewarded?
But if a person is late because of an excuse , and he enters the mosque when the prayer had ended, then the reward for praying in congregation will be decreed for him even if he prays alone.
Abu Hurayrah (may Allah be pleased with him) narrated that the Messenger of Allah (peace and blessings of Allah be upon him) said: “If a person does Wudu’ and does it well, then sets out for the mosque but finds that the people have already prayed, Allah will decree for him a reward like that of those who prayed and were present, and that will not detract anything from their reward.” (Narrated by Abu Dawud, 564 and An-Nasa’i, 855; classed as authentic by Al-Albani in Sahih Abu Dawud)
In `Awn Al-Ma`bud (2/192) it says: “This applies if the delay did not stem from any shortcoming.” (End quote)
And Allah knows best.