A donor may not claim a deduction for any contribution of cash, a check, or other monetary gift made on or after Jan. 1, 2007, unless the donor maintains a record of the contribution in the form of either a bank record (such as a cancelled check) or a written communication from the charity (such as a receipt or a letter) showing the name of the charity, the date of the contribution, and the amount of the contribution.
Publication 1771 , Charitable Contributions, Substantiation and Disclosure Requirements
Publication 526 , Charitable Contributions
Notice 2006-110: Record-keeping requirements for charitable contributions made through payroll deductions.
Notice 2008-16: Rules for substantiating lump-sum charitable contributions made through the Combined Federal Campaign or a similar program (e.g., a United Way campaign).