Abd al-Rahman bin Ka'b bin Malik (may Allah be pleased with them both) narrates from his father that whenever the Prophet (peace and blessings be upon him) intended a campaign, he would use tawriyah (concealing his true destination), and he would say: "War is deception."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب السير / 18451