Ask for a positive reference, not just a reference
This wording lets a hesitant person decline before their uncertainty reaches the employer. Remind them of your role, dates, and strongest work together.
Provide the decision context
Share the job description, deadline, contact method, current resume, and two or three relevant achievements. Do not script praise or hide a concern they are likely to be asked about.
Close the loop afterward
Thank them, tell them the outcome, and keep their details private. If they decline, accept it promptly and ask someone whose support is clearer.