Terminating a 50 Ohm source into 1M Ohm oscilloscope input
If you don't have access to a \$50 \Omega\$ feedthrough terminator, a T-connector with a \$50 \Omega\$ termination should work just as well. This was standard practice at my old company when we used external hall-effect current probes with our \$1 M\Omega\$ scopes. 

(Aside: I personally prefer using external \$50 \Omega\$ terminators even if the scope supports \$50 \Omega\$: they're usually capable of handling more power, and if you accidentally hook up something incorrectly, at least you're blowing an inexpensive and easily-replaceable component vs. necessitating a potentially expensive scope repair!)