I came to God’s Messenger when he was praying and sat down, but did not join the congregation in prayer. When he finished he saw me sitting and asked, “Have you not become a Muslim, Yazid?” I replied, “I certainly have become a Muslim, Messenger of God.” He asked, “What prevented you from joining the people in their prayer?” I replied, “I had already prayed at home, thinking you had prayed.” So he said, “When you come to prayer and find the people praying, pray along with them. If you have already prayed it will be a supererogatory prayer for you, though this is a prescribed prayer.”
Ibn ‘Umar said that a man questioned him saying, “When I pray in my house and then come to the mosque in time for prayer along with the imam, should I pray along with him?” He replied, “Yes.” The man asked which of them he should consider his obligatory prayer, and Ibn ‘Umar replied, “Is that your affair?* that is only to be left to God’s decision who will appoint whichever He wishes.”
*The Arabic is in the form of a statement, but in view of the phrase immediately following it seems necessary to treat it as a question.
Narrated A man of Asad b. Khuzaima said he put this question to Abu Ayyub al-Ansari:
I* pray at home and then go to the mosque and the time to begin the prayer comes, so I pray along with the congregation, but I feel some uneasiness about that. Abu Ayyub replied, “We asked the Prophet about that and he said that such a person gets a portion of the reward for corporate prayer.”
* The Arabic has “One of us prays . . . then goes . . .” After that the first person singular is used. While such a construction is quite usual in 'Arabic, it makes impossible English, so I have used the first person all through.
We came to Ibn ‘Umar at al- Balat* when the people were praying, and I remarked on the fact that he was not praying along with the people. He replied that he had already prayed and that he had heard God’s Messenger say, “Do not pray a prayer twice on the same day.”
* A square paved with stones between the Prophet's mosque and the market-place in Medina.