Ata (may Allah have mercy on him) said that Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) was invited to a meal while he was busy managing the water-supply (siqayah). He said to the people: "Go to your brother," or: "Accept your brother's invitation, convey my greeting of peace (salam) to him, and tell him that I am busy."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14540
Ata, or someone else, said: The messenger of Ibn Safwan came to Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) while he was busy tending to Zamzam. He invited him and his students, so he sent his students off and excused himself, saying: "If he does not accept my excuse, I will come too."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14541
Mujahid said that Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) was invited to a meal one day, and a man among the people said: "May I not be excused from this?" Ibn Umar (may Allah be pleased with them both) said: "There is no excuse for you; come along."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصداق / 14542