Greetings of the day!
My name is ___________ (name) and I am writing this email in reference to the previous email which was sent by me on __/__/____ (date) at __:__ (time) with subject line __________ (mention subject). I regret to inform you that I forgot to attach the documents along with the email sent earlier. Therefore I am sending you this email along with the pending documents.
You are requested to check the attachments sent along with this email and apologize for the delay. I expect you kind response in this regard.
____________ (Your name),
____________ (Contact details)