Ikrimah (may Allah have mercy on him) reports from Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) that he said: We shortened (the prayer) with the Prophet (peace and blessings be upon him) for nineteen days on a journey. And he said: If we stayed longer, we would pray the complete prayer.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الصلاة / 5459