God appeared to Abraham in the planes of Mamre, when he sate in the tent when Abraham lifted his eyes he looked three men stood by him, he ran to meet them and bowed himself towards the ground and requested them not to go away from that place. he fetched some water to wash there feet and asked to take rest under the tree. Abraham took butter and milk, and a dressed calf and put before them God had that food.
God remembered Sarah and promised a son to Sarah, but Sarah laughed at God because she is very old woman and her husband is also very old, it is impossible to have a child at that age but God made it possible, nothing is impossible for God.
The men ( Father - Son - Holy spirit ) started towards Sodom, God wanted to disclose the purpose of going to Sodom, God said to Abraham the cry of Sodom and Gomorrah is great, and their sins are very grievous. Abraham asked God weather he is going to destroy righteous along with the wicked. God said to Abraham if he finds 50 righteous in the city, the city will not be destroyed. Abraham again and again asked God by reducing the number of righteous from 50 to 45, 45 to 40, 40 to 30, 30 to 20 Abraham finally not to destroy the city if 10 righteous are there and God agreed not to destroy the city for the sake of 10 righteous.
" Abraham prayed God for himself and his family in the same manner for the people of Sodom and Gomorrah he prayed God a lot. Likewise we should also pray for others first there after ourselves. "
~ Genesis Chapter 18