Mishkat al-Masabih 3425
Abul Ahwas ‘Auf b. Malik quoted his father as saying:
I said, “Messenger of God, tell me what I should do about a cousin of mine to whom I go and ask for something, but who neither gives me anything nor regards my kinship, then when he needs my help comes to me and asks for something, and I have sworn that I would not give him anything or regard his kinship.” He commanded me to do that which is better and make atonement for my oath. 
In Ibn Majah’s version he told that he said, “Messenger of God, my cousin comes to me and I swear that I will not give him anything or regard his kinship,” and that he replied, “Make atonement for your oath.”

Nasa’i and Ibn Majah transmitted it.
عَوْفِ بْنِ مَالِكٍ عَنْ أَبِيهِ قَالَ: قُلْتُ: يَا رَسُولَ اللَّهِ أَرَأَيْتَ ابْنَ عَم لي آتيه فَلَا يُعْطِينِي وَلَا يَصِلُنِي ثُمَّ يَحْتَاجُ إِلَيَّ فَيَأْتِينِي فَيَسْأَلُنِي وَقَدْ حَلَفْتُ أَنْ لَا أُعْطِيَهُ وَلَا أَصِلَهُ فَأَمَرَنِي أَنْ آتِيَ الَّذِي هُوَ خَيْرٌ وَأُكَفِّرَ عَنْ يَمِينِي. رَوَاهُ النَّسَائِيُّ وَابْنُ مَاجَهْ وَفِي رِوَايَةٍ قَالَ: قُلْتُ: يَا رَسُولَ اللَّهِ يَأْتِينِي ابْنُ عَمِّي فَأَحْلِفُ أَنْ لَا أُعْطِيَهُ وَلَا أَصِلَهُ قَالَ: «كَفِّرْ عَنْ يَمِينِكَ»