Are we permitted to observe prayer (Salat) behind non-Ahmadi Muslims and Ahmadi Muslims who have not done bai‘at?

The Promised Messiah ^as was asked about observing prayer behind Muslims who are unaware of Ahmadiyyat. Hudur^as said:

Firstly,  there is no place where people are not aware, and if it is the case that people are unaware of us, then present our Movement to them. If they accept it then you can pray behind them. Otherwise not at all; pray alone. At this time, God Almighty wishes to prepare a Community. To then deliberately mix with those people who He wants to distinguish us from is against the purpose of God.

(Fatawa Hadrat Masih Mau‘ud, p. 27)

The Promised Messiah ^as was asked about observing prayer behind people who do not say that he as is a disbeliever or liar. Hudur^as said:

If they hypocritically do this, as some people have the habit of being Muslim with Muslims and Hindu with Hindus. They should proclaim that, “We neither consider him as a liar nor a disbeliever, rather, we consider him as a righteous and saintly person, and we consider those who say that he is a disbeliever to be disbelievers themselves because they declare a believer to be a disbeliever.” Thus, we would know that they are truthful. Otherwise, how can we trust them and how can we issue an order to pray behind them? “Disregarding respect for ranks amounts to heresy.” One should be soft when it is appropriate to be soft and harsh when it is appropriate to be harsh. 

(Fatawa Hadrat Masih Mau‘ud, p. 25)

The Promised Messiah ^as wrote:

God Almighty has informed me that you are forbidden and absolutely forbidden to offer your prayers behind an imam who pronounced me a disbeliever or liar, or who is in doubt. Indeed, your imam should be one of yourselves. There is an indication of this in one aspect of the hadith of Sahih al-Bukhari: (He will be your imam and will be from among yourselves;)

(Tadhkirah, p. 498)

Hadrat Musleh Mau‘ud ^ra was asked about observing prayer behind Ahmadis who have not done bai‘at. He ^ra said that it is not forbidden to pray behind them, but there are conditions. If that Ahmadi who has not done bai‘at prays behind non-Ahmadis, or is in favor of praying behind non-Ahmadis, then it is not permissible to pray behind him. Also, asked about said this permission is only to be used out of necessity; it should not be made into a habit (Fatawa Hadrat Musleh Mau‘ud, vol. 1, p. 68).