Does performing congregational prayers at the workplace's prayer room for forty days fulfill the Hadith "Whoever prays for forty days in congregation," or must it be in the جامع (main mosque)?

If the prayer room at work is designated for prayer and the adhan is raised therein, then it has the ruling of a mosque, and congregational prayer within it is considered equal in virtue to others. Consequently, whoever prays therein in congregation for the duration specified in the hadith will attain the reward associated with that prayer, because the word "congregation" in the hadith is absolute, and the default is for an absolute term to remain absolute unless restricted by evidence.