Of Prayer, by John Calvin, tr. Henry Beveridge [1845], at sacred-texts.com
But although it has been said above (sec. 7, 27, &c.), that we ought always to raise our minds upwards towards God, and pray without ceasing, yet such is our weakness, which requires to be supported, such our torpor, which requires to be stimulated, that it is requisite for us to appoint special hours for this exercise, hours which are not to pass away without prayer, and during which the whole affections of our minds are to be completely occupied; namely, when we rise in the morning, before we commence our daily work, when we sit down to food, when by the blessing of God we have taken it, and when we retire to rest. This, however, must not be a superstitious observance of hours, by which, as it were, performing a task to God, we think we are discharged as to other hours; it should rather be considered as a discipline by which our weakness is exercised, and ever and anon stimulated. In particular, it must be our anxious care, whenever we are ourselves pressed, or see others pressed by any strait, instantly to have recourse to him not only with quickened pace, but with quickened minds; and again, we must not in any prosperity of ourselves or others omit to testify our recognition of his hand by praise and thanksgiving. Lastly, we must in all our prayers carefully avoid wishing to confine God to certain circumstances, or prescribe to him the time, place, or mode of action. In like manner, we are taught by this prayer not to fix any law or impose any condition upon him, but leave it entirely to him to adopt whatever course of procedure seems to him best, in respect of method, time, and place. For before we offer up any petition for ourselves, we ask that his will may be done, and by so doing place our will in subordination to his, just as if we had laid a curb upon it, that, instead of presuming to give law to God, it may regard him as the ruler and disposer of all its wishes.