What is the ruling regarding a husband's request for his wife to abstain from a specific food or drink – such as Nescafe – out of concern for their infant son, especially given that there is one medical opinion that permits its consumption and another that recommends reducing it? And would the wife be sinful if she lied and swore by Allah that she did not drink it, in order to please her husband?

A husband is not permitted to prevent his wife from [doing] permissible things unless excessive engagement in them leads to harm. And harm must be repelled, whether the husband commands it or not. It is not permissible for a wife to lie or swear falsely, unless lying becomes the [only] means [to a permissible end]. She may use evasive language (ma'areedh) if she fears her husband. A wife should not insist on her opinion if there is flexibility in the matter and obeying her husband does not constitute disobedience to Allah.