He offers all the obligatory prayers in the mosque except for Fajr. What is the ruling on that?

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Check below answers in case you are looking for other related questions:
The evidence that it is obligatory to offer prayers in congregation in the mosque
Praying in scattered groups in a workplace musalla

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Related Answers:
He was praying a naafil prayer, then some other people prayed behind him, so he changed his intention to make it an obligatory prayer
He works as an accountant and does not pray in congregation occasionally because of that
Women in a house next to the mosque following the imam of the mosque in prayer
The evidence that it is obligatory to offer prayers in congregation in the mosque
Praying in scattered groups in a workplace musalla

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