Abdullah bin Umar (may Allah be pleased with them both) said that the Messenger of Allah (peace and blessings be upon him) said: "Two bloods and two dead things have been made lawful for us. The two bloods are the liver and the spleen, and the two dead things are fish and locusts."
Abd al-Rahman and his two brothers narrated it in this way from their father, while others narrated it as mawquf (a statement of Ibn Umar), and that is the correct version.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19697
Zayd bin Thabit (may Allah be pleased with him) said: I used to eat the spleen though I had no need of it, only so that my family would know that there is no harm in it.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19698
Ikrimah (may Allah have mercy on him) said: A man asked Sayyiduna Ibn Abbas (may Allah be pleased with them both): May I eat the spleen? He said: Yes. The man said: Most of it is blood. Sayyiduna Ibn Abbas (may Allah be pleased with them both) said: Only flowing blood is unlawful.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الضحايا / 19699