The story of Imam Ahmad hosting Imam al-Shafi'i (may Allah have mercy on both of them).

The Shaykh : They mentioned that al-Shafi'i (may Allah have mercy on him), Muhammad ibn Idris, stayed as a guest with Imam Ahmad. Imam Ahmad had been his student, and al-Shafi'i was his teacher. Ahmad often praised him in front of his family. So al-Shafi'i stayed as a guest with Imam Ahmad one night. They served him dinner, and he ate the entire meal. The people of the house were surprised that Imam al-Shafi'i ate the whole dinner, since the Sunnah is that a person should not eat more than a third of his stomach, yet he filled his stomach completely. That was the first thing. Then, (may Allah have mercy on him), he did not get up for the late-night prayer (tahajjud) as he usually did at the end of the night. What comes to mind is that someone like al-Shafi'i, a scholar of religion and a man of worship, is among those who perform tahajjud. But he did not get up for it. So the people of Imam Ahmad were surprised: why did he not get up for tahajjud? That was the second thing. When the call to the Fajr prayer was made, he went out without asking for water to perform wudu. They said, "This is the third thing." He went out to pray after having slept in his bed until morning without performing wudu. How is this possible, when deep sleep invalidates wudu? The people said, "The people of Imam Ahmad said to him: 'How can you speak so highly of al-Shafi'i when this is his condition?' He said: 'All right, I will bring you the news.' So he informed al-Shafi'i of this. Al-Shafi'i said: 'As for the food, I do not find in this city any food more lawful than the food of Imam Ahmad, so I wanted to fill my stomach with it.' There is no harm in a person filling his stomach sometimes.
'As for the fact that I did not get up for tahajjud, it is because I was reflecting on knowledge and the Sunnah, and seeking knowledge is better than tahajjud.' This is indeed the case; seeking knowledge is better than tahajjud. What was he reflecting on? He said, "I was reflecting on the saying of the Messenger (peace and blessings be upon him): Abu 'Amir was a small child in the city, and he had a bird called a naghir. A naghir is a small bird resembling a sparrow. Abu 'Amir used to play with it and was happy with it. Then the naghir died. The child was sad about the death of his bird, not happy. He was visibly sad. So the Messenger (peace and blessings be upon him) would joke with the boy, saying: 'So I reflected on this hadith and found [something], and I derived great benefits from it.' Some said: 'He derived two thousand benefits from this hadith.' But naturally, when he mentioned a benefit, he would provide evidence for it from the hadith or the Qur'an, and he would derive benefits from that evidence, so the benefits multiplied.