Malathion is just about one of the worst chemicals in the garden. Every hear of the atomic bomb? Are you getting headaches and do you wash your hands after using malathion?
Try mixing up some soapy water and using a spray bottle to spray the aphids. Malathion doesn't just kill aphids, it kills bees, hummingbirds, butterflies, and so on.
Google malathion and read the MSDS hadzard warning, you might be amazed.

God, I hope you wore a mask when you were spraying that stuff!
DOn't use that poison on yourself and your plants!
Listen to hibiscuslover above!

If you read and follow the instructions YOU will do just fine. I spray it just before sun down so it dries while the bees and birds sleep. Nothing has changed so it is still safe to use if you follow instructions.

You can spray aphids with a good solution of green soap and water. Kills many of our pest as it washs off their waxy coating. Spray them direct as it will kill other good bug also.

Last month my 2 hibiscus had more aphids on the blooms and new growth than I had ever seen. Fortunately I had found some Cygon a systemic insecticide at a garden center. I hear it was supposedly taken off the market but they had it so I bought it and put 1 tablespoon per gallon of water.
Poured about a half gallon at the roots and within 3 days all the aphids were dead. I would always recommend a systemic before spraying an insecticide. Rubbing alcohol also will kill aphids when it gets on them. Hope this helps.

I have 3 hibiscus plants that are being eaten up and yellowing from (white flies. ?) I was told malathion at garden store. Should I use? or someone help please before they die.

Read the above advise on cheap dish soap diluted with water in a spray bottle. It's cheap, safe and easy. Spray in early morning OR at night after dinner. Easy Peasy, and you won't kill anything bu the soft bodied insects that are eating your leaves.

How much soap and water please?