[If] one built a new house, or purchased new utensils, he says: ‘‘Blessed . . . Who has kept us alive.’’ One recites a blessing on a calamity which has an aspect of good, and on a favora-ble occurrence which has an aspect of bad. [If] one prays regarding the past, this is a prayer in vain. How so? [If] one’s wife was pregnant, and he said, ‘‘May it be [God’s] will that my wife give birth to a male,’’ this is a prayer in vain. [If] one was coming along the road, and he heard the sound of screaming in the city, and he said, ‘‘May it be [God’s] will that those [who are screaming] not be [members of] my household,’’ this is a prayer in vain.