It is known that the aqiqah for a male newborn comprises slaughtering two sheep. Is it permissible for a person who is unable to afford the price of two sheep at the time of the aqiqah to slaughter only one and delay the second until he is able to afford it? Please answer providing evidence and opinions of scholars.

In Islamic law, the aqiqah is the sacrifice made for the newborn, whether male or female. It is an established Sunnah that the Prophet (peace and blessings be upon him) and all the Companions (may God be pleased with them) practiced. Al-Tirmidhi, Abu Dawud, Al-Nasa`i and Ibn Majah reported through Ibn Abbas (may God be pleased with them both) that the Prophet (peace and blessings be upon him) sacrificed a sheep for each of his grandsons, Al-Hasan and Al-Hussein, when they were born. The sacrifice must be made on the seventh, fourteenth or the twenty-first day after the child’s birth. If this is not possible, it can be done on any day until the child attains puberty.
The Shafi'is and Hanbalis are of the view that it is recommended to slaughter two sheep for a male baby and one sheep for a female baby. This is based on the report of Aisha (may God be pleased with her) who narrated that the Prophet (peace and blessings be upon him) said: "Slaughter two similar sheep for a male newborn and one for a female" [recorded by Ahmad and Al-Tirmidhi who declared it authentic]. It is permissible to slaughter one sheep for a male baby when one cannot afford two.

Some hadiths mentioned the Prophet (peace and blessings be upon him) as sacrificing one sheep for each of his grandsons and based on this, Hanafi and Maliki scholars deemed it permissible to slaughter one sheep for both male and female newborns following the Prophet’s example.

The narration that mentions slaughtering one sheep states that the Prophet (peace and blessings be upon him) deemed it permissible to slaughter one sheep for a male newborn and this achieves and fulfills the Sunnah to facilitate the matter and remove hardship. As for the hadith narrated by Aisha (may God be pleased with her) in which the Prophet (peace and blessings be upon him) said: "Slaughter two similar sheep for a male newborn," narrators and exegetes stated that it referred to slaughtering the two sheep at the same time. However, the preponderant opinion is that it means that two sheep must be similar in age, weight etc. and that there is no objection to slaughtering only one and delaying slaughtering the other until it becomes affordable. For this reason, some scholars mentioned the different narrations on whether the Prophet (peace and blessings be upon him) slaughtered one or two sheep for each of his grandsons. Al-Mula Ali Al-Qari stated in his commentary on Mishkat Al-Masabeeh that the hadith illustrates the permissibility of slaughtering one sheep and that it is not obligatory to slaughter two sheep on the seventh day after the newborn’s birth. This means that a person may slaughter a sheep on the day of child’s birth and a second on the seventh day, thus reconciling between the different narrations.

It may also mean that the Prophet (peace and blessings be upon) slaughtered a sheep from his own money and ordered Ali or Fatimah to slaughter the other from their money.
And God the Almighty knows best.