One can follow the imam of a congregational prayer who is performing the qaḍāʾ of his own or someone else’s daily prayer about which he is certain.
However, if he is performing such a qaḍāʾ prayer as a precautionary measure [as opposed to being certain about it being a qaḍāʾ prayer], then it is not permitted to follow him unless the follower is also performing his prayer as a precautionary measure and the reason for his precaution is the same as that of the imam’s;[1] and if the follower has another reason for his precaution as well, he can still follow.