La taqum feehi abadan lamasjidun ossisa AAala attaqwa min awwali yawmin ahaqqu (surah Tawbah: 108)

Tafseer Tafheem-ul-Quran by Syed Abu-al-A'la Maududi

(9:108) You should never stand in that building: the Mosque which has been founded on piety from the very first day, is the proper place for you to stand (for prayer). For there are such people in it as would like to keep themselves pure; and Allah likes those people who like to keep themselves pure. *102

Laa taqum feehi abadaa; lamasjidun ussisa `alat taqwaa min awwali yawmin ahaqqu an taqooma feeh; feehi rijaaluny yuhibbona ai yatatahharoo, wallaahu yuhibbul mmuttah hireen

*102) " . . the one in conflict . . . Messenger" was Abu `Amir who belonged to the clan of Aus of AI-Madinah. He had become Christian monk during the period of `ignoranc' before the migration of the Holy Prophet and was well-known as a scholar of the Scriptures and was held in great reverence as a pious monk. But his scholarship and asceticism, instead of leading him to the Truth, became hindrance in the way. That was why he not only rejected Islam but also became a bitter enemy of the Holy Prophet and his Mission, for he took the Prophet for a rival in the "holy business" of priesthood. At first he ignored the Holy Prophet and his Mission in the hope that the power of the Quraish would suffice to crush him and his Mission. But when the Quraish suffered an utter defeat in the battle of Badr, he could no longer ignore it, so he started a vigorous vicious campaign against the Islamic Movement. Accordingly he left Al-Madinah and visited . different clans, in order to incite them against Islam, and was one of those who brought about the battle of Uhd. It is said that he had got some pits dug in the battle-field of Uhd, and that the Holy Prophet fell into one of these and received injuries. Then he played an important role in organizing the armies which came to invade Al-Madinah in the battle of Ahzab. Likewise this Christian Monk took a very active part in giving support to the mushriks against Islam in all the subsequent battles up to the battle of Hunain, At last when he realized that no power in Arabia could withstand the onslaught of lslam. he left Arabia and went to the Roman Caesar in order to warn him of the rising "danger" from AI-Madinah. It was because of his efforts that the Caesar began to make preparations for invading Arabia, to counteract which the Holy Prophet went forth on the expedition to Tabuk.
Now let us consider the background of the building of the `mosque' that was built to harm the Righteous Mission.
A section of the hypocrites of AI-Madinah collaborated wholeheartedly with Abu `Amir in all the above-mentioned hostile activities against Islam. They also fully agreed with him that he should use his "spiritual" influence to obtain military help from the Roman Caesar and the Christian states of northern Arabia. Accordingly, when he was preparing to go to the Roman Caesar to urge him to invade Arabia. they devised a plan of making a `mosque' of their own to serve as a safe meeting place for organizing themselves into a separate party because none would suspect that they were carrying on evil activities under the garb of religion. Moreover. this `mosque' would serve as an ambush for the agents of Abu `Amir who could stay in it as travellers and mendicants without raising any suspicion that they were spies of the enemy.
As there were already two mosques in Al-Madinah-one at Quba and the other, Masjid-i-Nabavi, in the city obviously there was no need for a third one. The hypocrite's themselves understood this: therefore they began to invent "reasons" to show that there was really a need for a third mosque. Accordingly, they went to the Holy Prophet and said, "We need another `mosque' because it is very difficult for the people of this area, especially the old, the sick and the disabled, to offer the five prescribed Prayers in either of the two Mosques, during the winter season and the rainfall. Therefore we intend to build a new `mosque' only for the convenience of those who live at a distance from the two Mosques but are desirous of saying their prayers in congregation."
With such professedly pure motives, these mischief makers built the 'mosque' and then went to the Holy Prophet with the request, "Sir, please stand in this new 'mosque' and lead the congregation in one of the prescribed prayers so as to perform its opening ceremony." But the Holy Prophet postponed the matter, saying, "At this time I am wholly engaged in making preparations for the expedition to Tabuk. I shall consider the matter on my return home. " After this he went forth to Tabuk, and they started their nefarious activities. They went on organizing themselves and conspiring against Islam in the `mosque' and decided to crown Abdullah-bin-Ubayy as their king, as soon as the Muslims would meet with reverses and be utterly crushed down by the Romans, as they had expected. But their expectations were all frustrated by what happened at Tabuk. Then on the revelation of these verses during the return journey at a place, Zi Avan, near AI-Madinah, the Holy Prophet despatched some men to demolish the mosque' before his entry into the city.