Why are there dots over some of the letters of the word אליו?
(18,9) “And they said to him: Where is Sarah, your wife? And he said: Behold, in the tent.”
Rashi comments that the word אליו has dots over the letters איו, and R. Shimon ben Elazar taught in Bereishis Rabbah 48:15 that wherever the written (the undotted) letters outnumber the dotted letters, you expound the written letters, and wherever the dotted letters outnumber the written letters, you expound the dotted letters. Thus, here where the dotted letters outnumber the written letters you expound the dotted letters - איו (where is he?) - and thus we learn that the angels also asked Sarah “Where is Avrohom?”. We learn from this that a person should inquire of his host - asking the man about his wife, and the woman about her husband.
Question: Since R. Shimon ben Elazar taught that words that have dots over some of the letters are expounded according the majority, if the Torah had put only one dot over the letter ל we still would have expounded the letters איו. So why did the Torah choose to put dots over the three letters איו?
The Chizkuni answers that if a dot had been placed only over the ל it would have implied that they first asked Sarah about Avrohom and then asked Avrohom about Sarah, because this is the order of the two words איו איה (where is he, where is she) in the posuk. But this is not true - first they saw Avrohom and only later around the time of the meal did they see Sarah. Therefore the dots were placed over the letters איו, because the dots indicate that the dotted letters do not belong in their current place, as Rashi explains in Devarim 29:28. Thus we learn that the angels did not ask according to the written sequence of the words, but rather they first asked Avrohom “Where is Sarah?” (איה) and afterwards they asked Sarah “Where is Avrohom?” (איו).
Another answer to this question can be found in the sefer Binyan Ariel.
The Ba’al HaTurim comments on this posuk that the words ויאמרו אליו (and they said to him) have the same gematria as אמרו אליה איו (they said to her: Where is he?).
The Kli Yakar asks that since Avrohom was standing right there, why did the angels need to ask Sarah where he was? See there for his explanation.
Rashi continues: The gemora in Bava Metzia 87a writes that the angels knew where Sarah Imenu was, but they asked the question in order to show that she was modest, to endear her to her husband. R. Yossi bar Chanina taught that they asked the question in order to send her the "cup of blessing" - the cup of wine over which the blessings after the meal had been recited.
Finally, Rashi comments on Avrohom’s reply “Behold, in the tent” - because she is modest, and the Sifsei Chachomim explains that this was the acknowledgement that the angels had endeavored to elicit when they asked the question.
The Kli Yakar asks why it was necessary for the angels to draw Avrohom’s attention to Sarah’s modesty - surely he already knew that she was modest! See there what he answers.
The sefer Imrei Shefer explains why Avrohom added the word “Behold” in his reply.
The Ohr HaChaim explains that the reason why the angels asked where Sarah was, was in order to inform Avrohom that the announcement which they had come to deliver was for Sarah, and therefore Avrohom answered “Behold, she is in the tent” and can hear everything which you say to her.
The Seforno explains that the mission of the angels was to announce to Sarah that she will have a son so that she will rejoice and give thanks in order that the pregnancy will be more complete, because Avrohom had already been told by Hashem that he would have a son from Sarah.