Is one sheep sufficient for a male's 'aqiqah, or are two sheep necessary to attain the Sunnah? Can the two sheep be completed later, or is it better to complete one of them first? What is the difference between the sufficiency of the 'aqiqah and attaining the Sunnah?

"Aqiqa (the sacrifice made upon the birth of a child) is a confirmed Sunnah (Prophetic tradition). The Sunnah is to sacrifice two sheep for a boy and one sheep for a girl. It is permissible to suffice with one sheep for a boy. If someone has two sons and possesses two sheep, it is preferable that he perform the Aqiqa for each of them with one sheep."