The end of the first chapter of Sefer Shemot recounts the story of the Hebrew midwives and how they defied Paro's order to kill the male Jewish infants.
Verse 21 reads (Artscroll translation): And it was because the midwives feared God that He made houses for them.
The Hebrew is actually rather vague: vaya'as lahem batim ויעש להמ בתים .
We must ask: Who made? Who was it made for? What are houses? One of the complications is the masculine ending on the word lahem. The Torah throughout this story used the feminine endings when referring to the midwives, why would it suddenly switch to the masculine if the word lahem refers to the midwives?
Rashi says (Artscroll translation): He made houses for them - The houses of kehunah, the priesthood, and leviyah, the tribe of Levi, and royalty, all of which are called houses ... Kehunah and leviyah from Jochebed, i.e. Aaron and Moses, and royalty from Miriam who was an ancestress of King David. According to Rashi, the answers to the three questions are God made for the midwives dynasties. Houses are not to be understood literally.
Rav Saadia Gaon says (my translation): He made for them (feminine להן) houses, guarding them.
His answer to the questions would be God made for the midwives places for their protection.
Next let's look at the Rashbam (one of Rashi's grandsons). His approach is very different: And he made for them houses - to guard them lest they would go to the Jewish women giving birth. Rashbam understands that it was Paro who made houses for the midwives, that is he imprisoned them so that they could no longer aid the women in childbirth.
All three of these commentators understand that להם, despite its masculine ending, refers to the midwives. How can that be? The truth is, the Torah in other places uses masculine endings even when referring to a group of women. For example, see Bereshit 31:9, where a masculine ending is used even though the pronoun is referring to Rachel and Leah. It would seem that the general context of our verse leads these commentators to conclude that the pronoun refers to the midwives.
For a very different approach we can look at the comment of Rabbeinu Bachya.
And the explanation of the verse according the simple meaning: And it was when the midwives feared God more than they feared the king and they kept alive the male babies, and he made houses for the Jews, that is to say, he settled guards and placed an Egyptian house between every two Jewish houses so that they would not be able to hide the babies.
Rabbeinu Bachya understands the pronoun להם as being masculine. Therefore, he interprets the verse as Paro making houses for the Egyptians amongst the Jews in order to spy on the Jewish families.
