When should the imam turn his rida' around?

It was narrated from Abdullah bin Abi Bakr that:

He heard Abbad bin Tamim said: "The Messenger of Allah ﷺ went out and prayed for rain, and he turned his rida' around when he turned to the Qiblah."

أَخْبَرَنَا قُتَيْبَةُ، عَنْ مَالِكٍ، عَنْ عَبْدِ اللَّهِ بْنِ أَبِي بَكْرٍ، أَنَّهُ سَمِعَ عَبَّادَ بْنَ تَمِيمٍ، يَقُولُ سَمِعْتُ عَبْدَ اللَّهِ بْنَ زَيْدٍ، يَقُولُ خَرَجَ رَسُولُ اللَّهِ ﷺ فَاسْتَسْقَى وَحَوَّلَ رِدَاءَهُ حِينَ اسْتَقْبَلَ الْقِبْلَةَ .