Assalamualaikum ustaz. I just had a baby boy. If I want to perform the aqiqah for my baby boy, is it enough with just one goat?
Waalaikumussalam wrt. wbt.,
Alhamdulillah, praise and gratitude to Allah SWT for His countless blessings for us all. Praise and salutations to our beloved Prophet Muhammad PBUH, his family, companions, and all those who follow his footsteps until the Final day.
Definition of Aqiqah and Its Ruling
Aqiqah means the slaughtering of an animal for slaughter as a sign of gratitude due to the birth of a child accompanied by an intention and certain conditions. 
The ruling of performing aqiqah is sunnah muakkad for those who are capable.  Its original sanctioning is according to a hadith from Salman bin Amir al-Dhabbi RA where he heard Rasullullah PBUH said:
مَعَ الْغُلاَمِ عَقِيقَتُهُ فَأَهْرِيقُوا عَنْهُ دَمًا وَأَمِيطُوا عَنْهُ الأَذَى
“Along with a boy there is an ‘Aqiqah, so shed blood on his behalf, and remove injury from him.” 
It is sunnah to be performed on the seventh day of the birth of the child and one should also give the child a good name as well as shave the child’s head. This is based on the words of the Prophet PBUH from Samurah RA:
الْغُلاَمُ مُرْتَهَنٌ بِعَقِيقَتِهِ يُذْبَحُ عَنْهُ يَوْمَ السَّابِعِ وَيُسَمَّى وَيُحْلَقُ رَأْسُهُ
“The boy is mortgaged by his ‘Aqiqah; slaughtering should be done for him on the seventh day, he should be given a name, and his head should be shaved.” 
According to the above hadith, the time for it to be performed on the seventh day of birth is just sunnah. If there is anyone who’d want to perform it before the seventh day or after it, they will still receive the rewards of aqiqah according to madhhab Syafie. 
Syeikh Zakariyya al-Ansari stated in his book, that the time to perform aqiqah begins at the birth of the child until the child reached puberty. 
According to another hadith narrated by Buraidah bin Husoib al-Aslami RA:
الْعَقِيقَةُ تُذْبَحُ لِسَبْعٍ ، أَوْ أَرْبَعَ عَشرَةَ ، أَوْ أَحَدَ وَعِشْرِينَ
“Aqiqah is on the seventh, fourteenth and twenty-first day of birth.” 
Originally, it is sunnah to be performed on the seventh day of birth. However, if one isn’t capable to do so, then perform it on the 14th. If he is still isn’t capable, then perform it on the 21st. If he is still isn’t capable, then perform it on any day when he’s able to do so. This is also the opinion issued by Dar al-Ifta’ Mesir.
Some contemporary scholars of madhhab Syafie stated that for anyone who isn’t capable, then perform the aqiqah but then he is able after the seventh day, then it is no longer sunnah to perform aqiqah. While some Syafi’iyyah scholars said it is before the nifas (vaginal bleeding due to childbirth) is over. However, the rajih opinion in madhhab al-Syafie stated that the sunnah ruling remains until the child reaches puberty. After the child reaches puberty, it is sunnah for the child himself to perform aqiqah for himself.
The number of goats for aqiqah
Basically, regarding the number of goats for aqiqah for a baby boy, it is sunnah with 2 goats and 1 goat for a baby girl.
According to the statement of the Prophet PBUH, it is stated:
مَنْ وُلِدَ لَهُ وَلَدٌ فَأَحَبَّ أَنْ يَنْسُكَ عَنْهُ فَلْيَنْسُكْ عَنِ الْغُلاَمِ شَاتَانِ مُكَافِئَتَانِ وَعَنِ الْجَارِيَةِ شَاةٌ
“If anyone has a child born to him and wishes to offer a sacrifice on its behalf, he may offer two sheep for a boy and one for a girl.” 
According to the above hadith, originally the aqiqah of a baby boy is two goats while for a baby girl is one goat. This is the best manner for a person who wants to perform aqiqah.
Is it Sufficient to Perform Aqiqah for a Baby with Just One Goat?
As for regarding the issue asked, is it sufficient to perform aqiqah with just one goat for a baby boy? Thus, the answer is it is sufficient and permissible.
This is the opinion in madhhab al-Syafi’e as cited by al-Imam al-Syirazi in his book al-Muhazzab and the same is stated by al-Imam al-Nawawi in his book al-Majmu’.
This is based on a hadith from Ibn Abbas R.Anhuma:
أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم عَقَّ عَنِ الْحَسَنِ وَالْحُسَيْنِ كَبْشًا كَبْشًا
“God’s messenger sacrificed a ram on the seventh day for both al-Hasan and al-Husain.” 
According to the guidance of the previously discussed hadith, here we state that it is sufficient to perform aqiqah for a baby boy with one goat and perform the worship of aqiqah with sincerity to showcase the gratitude for the blessing of Allah SWT for granting our family with a child and certainly Rasullullah PBUH will be proud of them in the hereafter for the vast number of the Prophet PBUH’s ummah.
 See al-Mausuah al-Fiqhiyyah al-Kuwaitiyyah, 30/276
 See al-Majmu’ Syarh al-Muhazzab, 8/426
 Narrated by al-Bukhari (2839)
 Narrated by Abu Daud (1522)
 See al-Majmu’, 8/431
 See al-Ghurur al-Bahiyyah, 5/171
 Narrated by al-Baihaqi (19771) and al-Tabarani in al-Mu’jam al-Ausat (4882) and al-Mu’jam al-Saghir (723)
 See Mughni al-Muhtaj, 6/139
 Narrated by Abu Daud (2842)
 See al-Muhazzab by al-Syirazi, 1/438 dan al-Majmu’ by al-Nawawi, 8/429
 Narrated by Abu Daud (2841)