I guessed

That night, Xue Qianyu had dinner at the Gu family's house. His mother and consort Kang had been getting closer to Cai Xiaolian and her sisters-in-law recently, and the five of them had established a deep friendship at the Mahjong table.

Hence, whenever Xue Qianyu wanted to go home for dinner, he would eat at the Gu residence.

Madam Xue and consort Kang didn't eat for free. When they arrived, they had brought a cart full of tonics, enough for the three pregnant women of the Gu family to eat for the entire pregnancy.

After dinner, Gu shouxin called Xue Qianyu to the study and asked about the letter that the Peng family had received during the day.

"Second uncle, how did you know that great general Peng had received a letter?" Xue qianren was shocked.