Question:
If a person has been adopted and knows the true mother’s name, which name should be used to ask for complete healing in REFUEINU prayer in the Amidah?
Answer:
If he is sure about his true mother’s name he should use her name when praying for a “refuah shelemah.” It is preferable to use the mother’s name rather than the father’s name or the adopted parents name.
Sources:
The Zohar (Bereishis 84a, citing Psalms 86:16, “והושיעה לבן אמתך”) says that it’s better to pray using the most definite facts available. There can be a slight chance that the sick person isn’t really the son of the man who is assumed to be his father, but his mother’s identity is (almost) never in doubt.