Maymun bin Mihran narrates from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that when Sayyiduna Ja'far bin Abi Talib (may Allah be pleased with him) and his companions (may Allah be pleased with them) went to Abyssinia, they used to pray standing in the boat.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5491