If a person fails to reach the mosque and time of prayer in the mosque is now gone (the congregational prayer has been offered in the mosque), does he have to offer congregation at home or can he pray alone at home?
Bismillah Hir Rahmaan Nir Raheem
As Salaamu 3laykum,
I hope you are doing well. If the congregation has been completed at the mosque then it would be recommended to just pray with someone else who has not prayed. If you cannot find anyone then to pray by yourself at the mosque. Since it is the house of ALLAH (Glory Be To HIM) so there would be more benefits there then praying at home. But overall there is no obligation to pray alone in the mosque if you have missed the congregation.
Below is the ranking of what we as Muslim men would be obliged to follow if we are in a close enough proximity to the mosque. For more clarification please see here: https://islamqa.info/en/answers/38881/is-it-obligatory-to-pray-jamaaah-in-a-mosque-that-is-far-from-the-house
Ranking Due to Obligation (Provided he is close to enough to the mosque and he is a Muslim male
#1: Congregation Prayer is Required
Prophet (peace and blessings of Allaah be upon him): “Whoever hears the call to prayer and does not respond, his prayer is not valid, except the one who has an excuse.”
Narrated by Ibn Maajah, 793; also narrated by al-Daaraqutni and al-Haakim, who classed it as saheeh. It was also classed as saheeh by al-Albaani in Saheeh Ibn Maajah.
The Prophet (SAW) said, "No doubt, I intended to order somebody to pronounce the Iqama of the (compulsory congregational) prayer and then I would go to the houses of those who do not attend the prayer and burn their houses over them." (Bukhari)
#2: Congregation at home / work place / etc.
ALLAH Messenger (ﷺ) said, "The prayer in congregation is twenty seven times superior to the prayer offered by person alone." (Bukhari)
#3: Praying at home / workplace by yourself
“Indeed, those who believe and do righteous deeds and establish prayer and give Zakah will have their reward with their LORD, and there will be no fear concerning them, nor will they grieve.” (Quran, Chapter 2 verse 277)
Now after saying the above there is a narration I found but I don't know the level of authenticity. However, here is the narration:
Narrated AbuSa'id al-Khudri: Prayer in congregation is equivalent to twenty-five prayers (offered alone). If he prays in a jungle, and performs its bowing and prostrations perfectly, it becomes equivalent to fifty prayers (in respect of reward).
Abu Dawud said: 'Abd al-Walid b. Ziyad narrated in his version of this tradition: "Prayer said by a single person in a jungle is more excellent by multiplied degrees than prayer said in congregation." (Abi Dawud)
There is no source I have come across that says it is obligatory to pray in the mosque once you have missed the congregational prayer.
Have a nice day!