Is it considered ill-mannered for a student to ask a scholar for the number of another scholar specializing in a different field to consult him?

If a student's question to his shaykh about the phone number of another shaykh is considered, by custom, a lack of etiquette, or if it implies a lack of trust in his knowledge, then he must avoid it. However, if it is not considered as such, or if the scholar permits him to do so, then there is no harm in it.