From page 338, section 2…
…what is it to pray in faith?
It is not to believe that the very thing…that we pray for, shall be always given…the right method of acting thy faith in prayer, which must be taken from the nature of the promise thou puttest in suit…our faith is to be shaped by the promise. If that be absolute…then thy faith may expect the very thing promised; if otherwise, then thou art not to limit thy faith to the thing itself, but expect money for money-worth; health, or as good as health…An absolute faith on a conditional promise…is fancy, not faith.
To pray in faith is to ask of God, in the name of Christ, what he hath promised, relying on his power and truth for performance, without binding him up to time, manner, or means.