Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.105.

Section : Entering the Mosque After the Prayer Is Finished.

The author of al-Mughni states, “If one enters the mosque after the prayer is finished, he may make the azhan and iqamah. Ahmad’s practice, based on what al-‘Athram and Sa’eed ibn Mansur recorded from Anas, was to ask a person to make the azhan and iqamah, after which he would pray with (some people) in congregation. If a person wishes, he may pray without making the azhan and iqamah. Says ‘Urwa, “If you reach a mosque wherein the people have already prayed, you may base your prayer on their azhan and iqamah, as theirs are sufficient for those who come after them.” This was the opinion of al-Hassan, ash-Sha’bi and an-Nakha’i. Al-Hassan, however, said, “I prefer that he makes the iqamah. If he makes the azhan, he should do so in a low voice and not aloud, for some people may consider it out of place.”