Ibrahim bin Muhammad bin Talhah narrates that Sayyiduna Umar (may Allah be pleased with him) said: It is not fitting for women of noble lineage to be married except to their equals.
The Shaykh said: Imam al-Shafi'i (may Allah have mercy on him) said that the condition of a guardian in marriage exists precisely so that a woman does not marry someone who is not her equal. This whole arrangement exists only so that she cannot marry someone who is not her equal.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النكاح / 13762