Genesis 16 v1-5 shows a lack of faith from Abraham, instead of patiently waiting on the LORD he foolishly attempts to fulfil God's promise of a child through his own efforts.

Genesis 16:1–5

Sarai and Hagar

16:1 Now Sarai, Abram’s wife, had borne him no children. She had a female Egyptian servant whose name was Hagar. 2 And Sarai said to Abram, “Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children¹ by her.” And Abram listened to the voice of Sarai. 3 So, after Abram had lived ten years in the land of Canaan, Sarai, Abram’s wife, took Hagar the Egyptian, her servant, and gave her to Abram her husband as a wife. 4 And he went in to Hagar, and she conceived. And when she saw that she had conceived, she looked with contempt on her mistress.² 5 And Sarai said to Abram, “May the wrong done to me be on you! I gave my servant to your embrace, and when she saw that she had conceived, she looked on me with contempt. May the LORD judge between you and me!”

Footnotes

[1] 16:2 Hebrew be built up, which sounds like the Hebrew for children
[2] 16:4 Hebrew her mistress was dishonorable in her eyes; similarly in verse 5

(ESV)