Ibn Jurayj (may Allah have mercy on him) says: I heard Ibn Abi Mulaykah (may Allah have mercy on him) say: I saw Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both): when they had finished with the grave of Sayyiduna Abdullah bin al-Sa'ib (may Allah be pleased with him) and the people had got up and left it, Sayyiduna Ibn Abbas (may Allah be pleased with them both) stood, halted at it and supplicated for him.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الجنائز / 7066