Dua of Ka'b Ahbaar

Q: There was one sahabi who was a jew before, most probably Abdullah ibn Salaam or Kaab Ahbar (ra), who said if I did not read this particular dua, the jews would turn me into a donkey. Which dua is it?

Insect killers

Q: Is it permissible to use an electric/electronic device to kill off insects such as cockroaches, ants etc. Presumably such devices have a heating element under a plate and insects are literally roasted to death or simply electrocuted.

Salaah becoming qadha

Q: This morning I was going to wake for fajar and heard the namaz and saw someone else in the bathroom so I closed my eyes and waited. I didn't realise that I fell asleep and when I got back up it was still dark so I rushed to the bathroom to make wudhu. I am a very doubtful person so making wudhu takes some time but I am trying to get better and did it as fast as I could. When I came back I looked outside and it was still a dark blue and there was little  yellow in the far back so I quickly started praying. I didn't think it was that late as fajar happens around 6. I thought it might be 6:30 at the latest but after I prayed 2 sunnats I checked my phone and it was almost 7. So I finished my namaaz. I know it is bad to delay prayer and I didn't mean to. I am so worried I might have prayed in the forbidden time but I remember reading that if you didn't mean to delay fajar prayer you can pray as soon as you remember or wake up so did I do the wrong thing? How do I fix this?