And we should persevere in our prayer petition.
There are cases where God has withheld the answer to prayers just to test the perseverance of the intercessor. If the need is there, and if the answer would be to the glory of God, then nothing should interfere with the continued petition.
There are occasions too, when God may fully intend to answer the need, but the time is not yet right. Yet God has inspired the prayer, and expects us to patiently continue to ask. Some prayers fail of an answer through lack of perseverance.