Entering the mosque when the imam is standing

Whoever enters the mosque when the imam is reciting al-Faatihah should say the opening takbeer, then be silent until the imam has finished reciting al-Faatihah, because the person who is praying behind an imam is enjoined to listen attentively to the recitation of his imam, and his reciting the opening du’aa’ and seeking refuge with Allaah will distract him from listening attentively as he is enjoined to do. He should not let himself be distracted from that which he is enjoined to do. 

See Majmoo’ al-Fataawa, 23/280 

His view – that he should not recite the opening du’aa’ or seek refuge when his imam is reciting out loud – is the more correct of the two scholarly views on this matter, in sha Allah. It is the view favoured by Shaykh al-Islam Ibn Taymiyah (may Allaah have mercy on him) as stated in Majmoo’ al-Fataawa (22/341 and 23/271), because of the strength of the evidence. The Prophet (peace and blessings of Allaah be upon him) said: “The imam has been appointed to be followed, so when he says takbeer, then say takbeer, and when he recites, listen attentively.” Narrated by Muslim, 404; al-Nasaa’i, 921. 

When the imam has finished al-Faatihah, the person behind him may say the opening du’aa’, then pray for refuge with Allaah and recite the Basmalah and al-Faatihah. If he cannot recite the opening du’aa’ and prayer for refuge and recite before the imam starts to recite the next soorah, then he should not recite the opening du’aa’, because the opening du’aa’ is Sunnah; rather he should recite the prayer for refuge and al-Faatihah, because the Prophet (peace and blessings of Allaah be upon him) said with regard to reciting behind the imam: “Do not do anything but recite the Essence of the Qur’aan [al-Faatihah], for there is no prayer for the one who does not recite it.” Narrated by al-Tirmidhi, 311; classed as saheeh by al-Albaani in Saheeh al-Tirmidhi. 

This is according to the view that it is obligatory for the person who is praying behind an imam in a prayer where Qur’aan is recited out loud to recite al-Faatihah. The correct view is that it is obligatory for him, because of the general meaning of the words of the Prophet (peace and blessings of Allaah be upon him): “There is no prayer for the one who does not recite the Opening of the Book.” Narrated by al-Bukhaari, 756. This means that such a prayer is not valid. 

See also question no. 10995 

But if he enters the mosque and the imam is offering a prayer when Qur’aan is recited silently, then he should say the opening takbeer and recite the opening du’aa’ and prayer for refuge, then recite al-Faatihah if he thinks that he can complete it before the imam bows, so that he may earn the reward for reciting the opening du’aa’ and al-Faatihah. Otherwise he should focus on al-Faatihah after saying the opening Takbeer, and not recite the opening du’aa’, because it is more important to pay attention to that which is obligatory. 

See Mughni al-Muhtaaj, 1/257; Talbees Iblees, p. 161 

If the imam bows, the person praying behind him should leave the rest of al-Faatihah and bow with him, because he has only caught up with what he has recited, and he has caught up with the rak’ah, as is the case if he catches up with him when he is bowing. So in this case the obligation to recite al-Faatihah is waived, and he should not lag behind his imam in order to complete al-Faatihah, because the Prophet (peace and blessings of Allaah be upon him) said: “When he bows, then bow.” Narrated by al-Bukhaari, 378; Muslim, 414. 

Shaykh Ibn Baaz (may Allaah have mercy on him) said: 

Reciting the opening du’aa’ is Sunnah and reciting al-Faatihah is obligatory for the one who is praying behind an imam, according to the correct scholarly opinion. If you fear that you will miss al-Faatihah, then start with it, and if the imam bows before you have completed it, then bow with him and the rest of it is waived in your case, because the Prophet (peace and blessings of Allaah be upon him) said: “The imam has been appointed to be followed, so do not differ from him. When he says takbeer, then say takbeer; when he bows, then bow…” Agreed upon. End quote. 

Majmoo’ Fataawa Ibn Baaz, 11/243-244. 

And Allaah knows best. 

See Ahkaam Hudoor al-Masaajid, p. 139-141, by Shaykh ‘Abd-Allaah ibn Saalih al-Fawzaan.