Should one interrupt a supererogatory prayer or a voluntary circumambulation to pray over a deceased person?

The apparent meaning of the Hadith: "When the prayer is established, there is no prayer except the obligatory one," is that a supererogatory prayer should not be interrupted except for an obligatory prayer. Therefore, it should not be interrupted for the funeral prayer. However, if the worshipper does interrupt it, there is no harm, because it is permissible to interrupt a supererogatory prayer for a valid reason. Similarly, one who is performing a voluntary circumambulation (tawaf) may interrupt his tawaf for the funeral prayer, though it is better not to interrupt it.