Ibn Maajah (1887) narrated that ‘Umar ibn al-Khattaab said:

“Do not go to extremes with regard to the dowries of women, for if that were a sign of honour and dignity in this world or a sign of piety before Allaah, then Muhammad (peace and blessings of Allaah be upon him) would have done that before you. But he did not give any of his wives, and none of his daughters were given, more than twelve uqiyah. A man may increase the dowry until he feels resentment against her and says, ‘You cost me everything I own, and caused me a great deal of hardship’.”

Classed as saheeh by al-Albaani in Saheeh Ibn Maajah, 1532. 

“Do not go to extremes” means do not exaggerate in increasing the dowry. “A man may increase the dowry until he feels resentment against her” means, until he begins to hate her when he is still paying off the debts incurred because of this mahr because it is too hard for him, or whenever he thinks about the matter.  

From Haashiyat al-Sindi ‘ala Ibn Maajah.