Sayyiduna Abu al-Darda' (may Allah be pleased with him) narrated: The Prophet (peace and blessings be upon him) was asked about wealth received from the ruler. He (peace and blessings be upon him) said: "If Allah Almighty has given it to you without your asking and without greed, then take it and increase your wealth with it." Al-Hasan said: There is no harm in it, so long as the person has not travelled to seek that wealth, nor has greed for it in his heart. In one narration the words are: "Whatever Allah Almighty gives you through any of us without your asking, consume it (that is, take it)." Ahmad recorded all these narrations; its chain contains a narrator who has not been named.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الزكاة / 4558