I told my friend that she should check to see if her husband's job is Halal or not and that caused problems between them. Did I do something Haram by saying that to her?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If your intention from this information was to create troubles between the husband and his wife, and to cause mischief between them, then what you did is forbidden.

The Prophet said: “Whoever incites a slave woman against her master, or a wife against her husband, he is not one of us.” [Ahmad and Abu Daawood]

However, if your intention was not so, and the husband appears to be good from his external appearance, then you are not to advise his wife to assure his source of income. Because going deeply into other people's personal matters is prohibited in the Sharee’ah.

On the other hand, if his external appearance arouses doubts or indicates corruption, then asking your friend about it is permissible, and you may be rewarded if you did that act for the Sake of Allah.

Allah knows best.