Is legal ruqyah obligatory for someone who has learned it if requested of them, or is it merely recommended?

Scholars have stipulated the desirability of a Muslim performing ruqyah for his brother if he is able. It may sometimes become obligatory for him, such as when he is certain that his brother would perish without it. The evidence for this is the hadith of Jabir, may Allah be pleased with him: "Whoever among you can benefit his brother, let him do so," and "I see no harm in whoever is able to benefit his brother, so let him benefit him."