Is it valid for one who is praying an obligatory prayer to pray behind one who is praying a voluntary prayer?

The questioner : The questioner asks: Is it permissible to pray the obligatory prayer behind someone praying a voluntary prayer, such as praying the obligatory prayer while he is praying Tarawih? Or is it permissible to pray Tarawih as well? This date, is it possible? Is it possible? That the borrower comes. Welcome.

The Shaykh : For the one praying a voluntary prayer, meaning the imam is praying a voluntary prayer and the follower is praying an obligatory one. The questioner gave as an example a man who entered the mosque while the imam was praying Tarawih, and this entrant had not prayed the 'Isha' prayer. So, is it permissible for him to join the imam who is praying Tarawih while he completes his 'Isha' prayer? We say that Imam Ahmad (may Allah have mercy on him) explicitly stated the permissibility of this, and said that it is permissible for a person, if he enters while the imam is praying Tarawih and he has not prayed 'Isha', to join the imam with the intention of the obligatory prayer. Then, when the imam concludes the Tarawih prayer, he stands and completes the remainder of his 'Isha' prayer. This is what we base our ruling on from Imam Ahmad, and it is also the view of Shaykh al-Islam Ibn Taymiyyah. It is also what is indicated by the hadith of Mu'adh ibn Jabal (may Allah be pleased with him), for Mu'adh ibn Jabal used to pray the 'Isha' prayer with the Prophet (peace and blessings be upon him), then he would go to his people and pray that prayer with them, so it would be a voluntary prayer for them and an obligatory one for him. He did this during the time of the Messenger of Allah (peace and blessings be upon him). Some scholars said, and some scholars said, that it is not valid for one praying an obligatory prayer to pray behind one praying a voluntary prayer due to the difference in intention. They answered regarding the hadith of Mu'adh by saying that the Prophet (peace and blessings be upon him) was not aware of it. Our answer to this is: First, there is no evidence that a difference in intention between the imam and the follower is a condition. Second, the claim that the Messenger (peace and blessings be upon him) was not aware of Mu'adh's practice.
We say: Yes, there is a possibility that the Messenger (peace and blessings be upon him) was not aware of it, but this possibility is remote. Because Mu'adh (may Allah be pleased with him) used to pray with his people, so one night he began reciting Surat al-Baqarah, and a man from the Ansar entered and prayed alone. This affected Mu'adh, until the matter reached the Prophet (peace and blessings be upon him). The Messenger (peace and blessings be upon him) said: "Are you not being kind, O Mu'adh?" This is evidence that the Messenger (peace and blessings be upon him) had knowledge of this. Then I also say: Let us suppose that the Prophet (peace and blessings be upon him) was not aware of this. The All-Knowing, the All-Aware is amazed by this, and He is Allah. And the time was a time of revelation. If something had occurred that was not permissible, the Prophet (peace and blessings be upon him) would have clarified it, or Allah the Exalted would have clarified it to His servants. For this reason, the Companions (may Allah be pleased with them) used the fact that a man was separating from his wife while the Qur'an was being revealed as evidence for the permissibility of coitus interruptus. Meaning, if something were forbidden, the Qur'an would have forbidden it. So, this is a rule I give to students of knowledge: Whatever matters of worship occurred during the time of the Prophet (peace and blessings be upon him), whether we know that the Prophet (peace and blessings be upon him) was aware of them or not, they are valid. Because if we know that the Prophet (peace and blessings be upon him) was not aware of it but he approved it, it is a Sunnah of approval. And if we do not know, then the approval of Allah for it is sufficient for that. This is very important; a student of knowledge should adopt it because it is beneficial for a person. The Companions (may Allah be pleased with them) used it, as in the hadith regarding coitus interruptus while the food [revelation] was descending. Coitus interruptus from a woman for the purpose of evaluation so that the food [semen] does not enter. The meaning of coitus interruptus from her is that he withdraws from her. Coitus interruptus is when a man has intercourse with his wife and approaches ejaculation, he withdraws from her so that he does not ejaculate in the vagina, resulting in a child. This is coitus interruptus.
The important point is that the correct view is that a difference in intention between the imam and the follower does not affect the validity. For this reason, the Prophet (peace and blessings be upon him) clarified this by saying: "The imam is made to be followed, so do not differ from him. When he says Takbir, you say Takbir, and when he raises [his hands], you raise [yours], until the end of the hadith." He clarified that the intended meaning of "do not differ" is difference in actions and words in which following is commanded, and it is not intended to mean difference in intention. So, if you come and join him for the Tarawih prayer and you bow with him while you intend the obligatory prayer, you have fulfilled it. Then, when he completes his Tarawih, you give [complete] what remains of your prayer.