Imam al-Shafi'i (may Allah have mercy on him) said: "The rational basis of the view of Ata' (may Allah have mercy on him) on this is that he held that there is neither making up nor expiation owed by him."
Imam al-Shafi'i (may Allah have mercy on him) said: "Allah Almighty declared the vow regarding the bahirah and the sa'ibah (animals) void only because it is disobedience, and He did not mention any expiation for it, and the Sunnah has come in accordance with this."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / Q20056
Al-Qasim bin Muhammad narrates from Sayyidah Aishah (may Allah be pleased with her), the wife of the Prophet (peace and blessings be upon him), that the Messenger of Allah (peace and blessings be upon him) said: "Whoever vows to obey (Allah), let him obey Him; and whoever vows to disobey Allah, let him not disobey Him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20056
Sayyiduna Imran bin Husayn (may Allah be pleased with him) narrates from the Prophet (peace and blessings be upon him) that he (peace and blessings be upon him) said: "There is no vow in disobedience, nor in what the son of Adam does not own."
Imam al-Shafi'i (may Allah have mercy on him) said: In the narration of Abd al-Wahhab al-Thaqafi with this chain: A woman of the Ansar fled on a she-camel belonging to the Prophet (peace and blessings be upon him) and vowed that if Allah saved her on it, she would slaughter it. The Prophet (peace and blessings be upon him) said these words and took his she-camel.
Imam al-Shafi'i (may Allah have mercy on him) said: He (peace and blessings be upon him) did not order her to slaughter one like it, nor to give expiation.
Imam al-Shafi'i (may Allah have mercy on him) said: So we hold that whoever vows, as an act of piety, to slaughter someone else's property, the vow falls away from him; and whoever vows what he cannot do in any way, the vow falls away from him, because he has no power to do it, so it is like what he does not own.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20057
Ayyub bin A'idh al-Ta'i (may Allah have mercy on him) said: I said to al-Sha'bi (may Allah have mercy on him): "A man vowed that he would slaughter his son." He said: "It seems you are one of those who rely on analogy. I do not know anyone among the people who sought knowledge across the regions more than Masruq (may Allah have mercy on him)." He said: "There is no vow in disobedience."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 20058