1 Now the LORD appeared to him by the oaks of Mamre, while he was sitting at the tent door in the heat of the day. 2 When he lifted up his eyes and looked, behold, three men were standing opposite him; and when he saw them, he ran from the tent door to meet them and bowed himself to the earth, 3 and said, “My Lord, if now I have found favor in Your sight, please do not pass Your servant by. 4 “Please let a little water be brought and wash your feet, and rest yourselves under the tree; 5 and I will bring a piece of bread, that you may refresh yourselves; after that you may go on, since you have visited your servant.” And they said, “So do, as you have said.” Genesis 18:1–5 (NASB95)

1 God appeared to him near the oak of Mamre while he was sitting at the door of his tent during midday. 2 Upon looking up, he saw with his eyes, and look, three men had stood over him, and upon seeing them, he ran up from the doorway of his tent to meet them and he bowed down to the earth, 3 and he said, “Lord, if perhaps I have found favor before you, do not pass by your servant. 4 Let water now be taken, and wash your feet, and rest under the tree. 5 And I will take bread, and you will eat, and after this you will go on your journey, on which account you turned aside to your servant.” And he said, “Do so, just as you have said.” Genesis 18:1–5 (LES2)

6 So Abraham hurried into the tent to Sarah, and said, “Quickly, prepare three measures of fine flour, knead it and make bread cakes.” 7 Abraham also ran to the herd, and took a tender and choice calf and gave it to the servant, and he hurried to prepare it. 8 He took curds and milk and the calf which he had prepared, and placed it before them; and he was standing by them under the tree as they ate. Genesis 18:6–8 (NASB95)

6 And Abraham hurried to the tent to Sarah and said to her, “Hurry and mix three measures of the finest wheaten flour and make loaves baked in the ashes.” 7 And Abraham ran to the cattle and took a tender and fair little calf, and he gave it to the servant, and he hurried to prepare it. 8 He took butter and milk and the little calf that he prepared and set it before them, and they ate. He himself stood beside them under the tree. Genesis 18:6–8 (LES2)

9 Then they said to him, “Where is Sarah your wife?” And he said, “There, in the tent.” 10 He said, “I will surely return to you at this time next year; and behold, Sarah your wife will have a son.” And Sarah was listening at the tent door, which was behind him. 11 Now Abraham and Sarah were old, advanced in age; Sarah was past childbearing. 12 Sarah laughed to herself, saying, “After I have become old, shall I have pleasure, my lord being old also?” 13 And the LORD said to Abraham, “Why did Sarah laugh, saying, ‘Shall I indeed bear a child, when I am so old?’ 14 “Is anything too difficult for the LORD? At the appointed time I will return to you, at this time next year, and Sarah will have a son.” 15 Sarah denied it however, saying, “I did not laugh”; for she was afraid. And He said, “No, but you did laugh.” Genesis 18:9–15 (NASB95) 

9 He said to him, “Where is Sarah, your wife?” But he, replying, said, “Look, she is in the tent.” 10 He said, “When I return, I will come to you at the same time next year, and Sarah, your wife, will have a son.” Sarah heard this at the door of the tent, being behind him. 11 Abraham and Sarah were old, advanced in days. Menstruation had ceased for Sarah. 12 Sarah laughed to herself, saying, “Well, it has not yet happened to me up to now, and my lord is an old man.” 13 And the Lord said to Abraham, “Is it that Sarah laughed in herself, saying, ‘Then indeed, truly will I give birth? I have grown old.’ 14 Is the word impossible with God? I will return to you at this season, for the time, and Sarah will have a son.” 15 Sarah denied it, saying, “I did not laugh”; for she was afraid. And he said, “No, but you did laugh.” Genesis 18:9–15 (LES2)

Here we see some differences worth mentioning. Going with my opinion that the LXX is often a more literal rendering of the original Paleo-Hebrew text, it says that “menstruation had ceased” for her; whereas, the MT renders it more delicately as “Sarah was past childbearing.”

In verse 12, the MT records Sarah asking, “After I am old, shall I have pleasure…?” The LXX differs by her saying something more natural and, to me, believable – “Well, it has not yet happened to me up to now…” 

In verse 14, the MT has the Lord asking, “Is anything too difficult for the Lord?” which is a memorable saying for sure. The LXX records, “Is the word (Greek: rhema) impossible for God?” This is less poetic but is perhaps more authentic.

The rest of the passage agrees.