Did `Umar Ibn Al-Khattab Pray in a Church?
Question

When the Companions of the Prophet (blessings and peace of Allah be upon him) were in Al-Quds (Jerusalem), and they conquered the city, Sayyiduna `Umar ibn Al-Khattab (may Allah be pleased with him) was with them. When the noble Sahabah prayed in the courtyard of the church, at the invitation of the archbishop, `Umar ibn Al-Khattab did not join in with them for other reasons.
Is it true that the Sahabah prayed in the church?
Can you explain this matter to me?
Praise be to Allah.Did Umar ibn al-Khattab Pray in a Church?
There are no chains of narration in the books of the Sunnah and reports that we have read for the incident of `Umar ibn Al-Khattab (may Allah be pleased with him) praying in the church at the time of the conquest of Bayt Al-Maqdis. Similarly, there is no report from the Companions to suggest that they prayed in the church.
Why Did `Umar Not Pray Inside a Church?
The oldest report we have seen that mentions the details of the incident is the report of Ibn Khaldun (may Allah have mercy on him), which says that the reason why `Umar ibn Al-Khattab (may Allah be pleased with him) refused to pray in the church was the fear that the Muslims after him might take it as a mosque.
Ibn Khaldun (may Allah have mercy on him) said:
`Umar ibn Al-Khattab entered Bayt Al-Maqdis, and came to the Church of the Resurrection and sat in its courtyard. When the time for prayer came, he said to the patriarch: I want to pray. He said to him: Pray where you are. But he refused, and he prayed on the doorstep of the church, on his own. Then when he had finished praying, he said to the patriarch: If I had prayed inside the church, the Muslims after me would have taken it (as a mosque) and they would have said: `Umar prayed here. And he wrote for them that they were not to gather to pray on the steps and that Adhan was to be given from that location. (End quote from Tarikh Ibn Khaldun, 2/225)
Is There Proof That `Umar Prayed in a Church?
There is no chain of narration for this incident, so it is not permissible to attribute it to `Umar (may Allah be pleased with him).
It appears to us that the story’s text is inauthentic and it is not valid for two reasons:

The Muslims are not entitled to take a church if a Muslim ruler or an ordinary Muslim prays in it, and that view [which says that if a Muslim ruler prays in it, it becomes theirs] is not known to the leading jurists.
What is proven from `Umar (may Allah be pleased with him) is that he regarded it as permissible to pray in a church, if it is free of statues and images, but if there were such things in a church, `Umar ibn Al-Khattab would refuse to enter it, let alone pray in it.

`Umar (may Allah be pleased with him) said: We do not enter your churches because of the statues and images in them. (Narrated by Al-Bukhari, 1/167)
For more details, please see these answers:
Places Where Prayer Is Not Allowed
Can Muslims Pray in a Church?
Ruling on Muslim praying in the house of a Christian
Can Muslims Go to Church?
Ruling on using the church as a hall for activities for Muslim children
Ruling on renting churches
And Allah knows best.