Vowing to fast for three months if his brother is safe from Qisas

Q: My brother stabbed a person and was therefore sentenced to jail following a criminal lawsuit. Fearing that my brother could be subject to retaliation, I vowed to Allah to fast for three months if my brother was exempted from it. Praise be to Allah, the stabbed person was cured from his injury, and he got my brother out of jail. I would like to ask about the vow I made to Allah (Exalted be He) to fast for three months; am I obliged to fast, or should I feed needy persons according to the number that would be stipulated by your Eminence? Please provide me with the Fatwa on what is better for me, and what could save me before Allah (Glorified and Exalted be He). May Allah reward you well on our behalf and grant you success! It should be mentioned that I am breastfeeding now, and I have a report from my physician declaring that I should not fast these days. I hereby attach to your Eminence the medical report for further perusal.

A: You should fulfill your vow, for what is authentically reported that the Prophet (peace be upon him) said, Whoever (Part No. 23; Page No. 287) takes a vow to obey Allah should obey Him. And this vow you have made to offer Sawm (fast) is a vow of obedience. Yet, there is no problem in delaying fasting until you recover from the ulcer that you have. If this vow was made inside your mind without expressing it verbally, there will be nothing upon you due to the general meaning of his saying (peace be upon him), My Ummah was forgiven for the thoughts that occur to their minds, as long as such thoughts are not put into action or uttered. May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.