Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Messenger of Allah (peace and blessings be upon him) said: "Sulayman bin Dawud (peace be upon them both) said: 'Today I will go round to seventy women, and each one will give birth to a horseman who will fight in the path of Allah.' His companion said to him: 'Say "In sha' Allah" (if Allah wills).' But he did not say "In sha' Allah". Then he went round to all of them, and only one woman became pregnant, and she too gave birth to half a man. By the One in whose hand is the soul of Muhammad (peace and blessings be upon him), had he said "In sha' Allah", they would all have striven in the path of Allah."
(b) In the hadith of Abu Qatadah, concerning the story of the spoils (salab), the words of Sayyiduna Abu Bakr al-Siddiq (may Allah be pleased with him) in the presence of the Prophet (peace and blessings be upon him), 'La ha Allahi idhan', mean "By Allah".
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19909