Sayyiduna Abu Hurayrah (may Allah be pleased with him) said that the Prophet (peace and blessings be upon him) said: "Whoever adjures someone with an oath, thinking that he will fulfil his oath for him, but he does not do so, then the sin is only upon the one who did not fulfil it for him."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الأيمان / 19891